# How Birth Order Affects Your Future

An episode of [Dr Justin Coulson's Happy Families](https://invisiblenetwork.ai/podcast/1082244480), 19 Aug 2026, 14 min.

Audio: https://mgln.ai/e/187/traffic.omny.fm/d/clips/fa326977-3de5-4283-9b8b-af3500c58607/b69b2795-5503-4de1-ac91-af460017906e/d79f6de8-c854-43c4-8a08-b49a00b04af9/audio.mp3?utm_source=Podcast&in_playlist=a05f1702-0c0e-4b0f-8014-af460017907c

Firstborns tend to earn more, study longer and experience better mental health than their younger siblings. For decades, researchers have struggled to explain why. A huge study following 1.2 million Danish children has uncovered a surprising piece of the puzzle. It may have less to do with personality or favouritism and more to do with germs, early illness and the extra time firstborns get with their parents. In this episode, Justin and Kylie unpack what birth order research actually tells us, why the first six months matter so much, and the simple things parents can do to help level the playing field. KEY POINTS • Firstborns show small but consistent advantages in earnings, education and mental health across large population studies. • Younger siblings are more likely to be exposed to respiratory illnesses during their first year, often brought home by older siblings. • Early illness may explain a significant portion of the birth order gap. • Firstborns can receive thousands more hours of reading, talking and playing with parents by age 13. • Birth order is not destiny. These findings describe population averages, not what will happen to an individual child. • Parents can reduce some of these differences through illness prevention, connection and intentional one-on-one time. QUOTE OF THE EPISODE “Your youngest child is not doomed, your eldest is not blessed.” RESOURCES MENTIONED • Article in The Washington ACTION STEPS FOR PARENTS • Keep recommended immunisations up to date and discuss newborn protection with your healthcare provider. • Breastfeed if you can and if it works for your family. • Get older siblings washing their hands when they come home from school or daycare. • Keep sick siblings away from newborns, particularly during the first six months. • Make space for one-on-one reading, talking and play with younger children. • Forget the stopwatch. Aim to be available and connected rather than trying to divide your attention perfectly equally. See omnystudio.com/listener for privacy information.

## Transcript

[0:05] Speaker 1: This is The Happy Family Podcast. Firstborns earn more money
[0:10] Speaker 1: than later born kids, they study longer, they have better
[0:14] Speaker 1: mental health than their younger siblings, and the lady you're
[0:17] Speaker 1: born sorry, the worse it gets. For decades, nobody could
[0:21] Speaker 1: explain why. Now, new research following one point two million
[0:24] Speaker 1: Danish children has just cracked the birth order code and
[0:29] Speaker 1: the answer is not what anyone expected. It's not favoritism,
[0:32] Speaker 1: it's not personality. Half of it is germs today, why
[0:39] Speaker 1: birth order leaves a mark and the very fixable things
[0:43] Speaker 1: that parents can do about it. This is The Happy
[0:48] Speaker 1: Family's podcast, Real Parenting Solutions every Day, Australia's most downloaded
[0:51] Speaker 1: parenting podcast. Kylie, it's a doctor's desk episode that is
[0:55] Speaker 1: fascinating to me about birth order.
[0:58] Speaker 2: Okay, so I'm just gonna stop you right there, because
[1:00] Speaker 2: you have been very, very vocal over the years about
[1:03] Speaker 2: your absolute disbelief that birth order has any impact on
[1:08] Speaker 2: our children.
[1:09] Speaker 1: So I've never said it has no impact. I've said
[1:11] Speaker 1: that the impacts are overstated. And all of those books
[1:14] Speaker 1: are out there about how firstborns are the leaders and
[1:17] Speaker 1: the youngest of the coddled ones, and the middle children
[1:19] Speaker 1: get lost there's really not much, if any evidence to
[1:22] Speaker 1: support any of that sort of stuff, But there is
[1:24] Speaker 1: pretty good evidence on a range of other things, like
[1:27] Speaker 1: who's most likely to earn more money, who's more likely
[1:30] Speaker 1: to live longer, that kind of stuff.
[1:33] Speaker 2: Well, maybe my brain got muddled up because I clearly
[1:35] Speaker 2: am not earning enough money.
[1:37] Speaker 1: You are the firstborn. Do you have a job other
[1:41] Speaker 1: than doing this podcast with me?
[1:44] Speaker 2: No?
[1:44] Speaker 1: Okay, my point podcaster is not a Well, there are
[1:48] Speaker 1: a few people in the world that are making a
[1:49] Speaker 1: lot of money from podcasting. We do it because we
[1:51] Speaker 1: love and we know it's helpful. Is it not payment
[1:54] Speaker 1: enough for you?
[1:54] Speaker 2: No? Definitely not if this research is suggesting that I
[1:58] Speaker 2: should be earning way more. All right, let's get serious.
[2:02] Speaker 2: What is the research telling us? Now?
[2:04] Speaker 1: Okay, so here's the overview. There was a big study
[2:08] Speaker 1: in two thousand and five, and what it found is
[2:11] Speaker 1: that younger siblings do worse than firstborns on lifetime earnings,
[2:17] Speaker 1: on education, and on mental health. Now, I'm not going
[2:21] Speaker 1: to get you to say this out loud. Well, I
[2:23] Speaker 1: was just thinking, but do the checklist against you and
[2:25] Speaker 1: any siblings that you have, and I'm doing it the
[2:27] Speaker 1: same for me. In terms of lifetime earnings, in terms
[2:31] Speaker 1: of who's the most educated. Can we combine and mental health?
[2:37] Speaker 1: I want to tread really carefully here, but there is
[2:39] Speaker 1: research that points in that direction. You can make your
[2:42] Speaker 1: own self assessment based on what's happening in your family. Oh, incidentally,
[2:45] Speaker 1: this isn't a guarantee. It's not saying every firstborn child's
[2:48] Speaker 1: going to do better than their siblings, clearly because I'm
[2:51] Speaker 1: the firstborn as well. So if you're listening to this
[2:54] Speaker 1: and you're a later born child and you're like, I
[2:58] Speaker 1: smashed my big brother, that's fine on you. Look, you
[3:02] Speaker 1: beat the odds. That's what I'm okay. And for women,
[3:07] Speaker 1: the research shows as well. Younger siblings do worse when
[3:10] Speaker 1: it comes to teen pregnancy rates, and every step down
[3:15] Speaker 1: the birth order the outcomes slide.
[3:18] Speaker 2: Okay, So I am ridiculously curious because you've articulated very
[3:22] Speaker 2: clearly that it has nothing to do with favoritism. It's
[3:26] Speaker 2: not because mum and dad spent more time with the
[3:28] Speaker 2: firstborn and gave them more quality education opportunities. Right, So
[3:33] Speaker 2: what is it you said?
[3:35] Speaker 1: One of the biggest theories has always been around parental
[3:38] Speaker 1: investment in the child.
[3:39] Speaker 2: Yeah, well, I know just from personal experience with number one,
[3:43] Speaker 2: I didn't have anyone else to worry about, y, so
[3:46] Speaker 2: I got to give her all of my time. And
[3:49] Speaker 2: then once the next two and three came along, because
[3:51] Speaker 2: they happened pretty fast, I ate.
[3:54] Speaker 1: A lotless investment. I'm to worry about children five and
[3:57] Speaker 1: six in our family. I'm just going to say.
[3:58] Speaker 2: It wasn't because I didn't want to though.
[4:00] Speaker 1: No, no, no, it was just lack of your pastor Yeah, yeah, totally. So.
[4:05] Speaker 1: There's an economist by the name of Joe Price two
[4:06] Speaker 1: thousand and eight did a big study on firstborn's found
[4:09] Speaker 1: that they get twenty to thirty minutes more per day
[4:13] Speaker 1: of quality time than second born children at the same age.
[4:16] Speaker 2: Well, I first probably steals that every day as well. Yeah,
[4:19] Speaker 2: so that even now she's twenty seven.
[4:21] Speaker 1: You do the maths on that, though, That compounds to
[4:23] Speaker 1: three thousand extra hours of reading and playing and talking
[4:28] Speaker 1: by the time that child is just thirteen. So that's
[4:31] Speaker 1: like a year of full time parenting that the younger
[4:34] Speaker 1: child never receives.
[4:35] Speaker 2: But you're saying that actually doesn't have anything to do
[4:37] Speaker 2: with this.
[4:38] Speaker 1: Well, no, I'm not saying it doesn't have anything to
[4:39] Speaker 1: do with it. I think that it's a really strong
[4:41] Speaker 1: hypothesis and it's worthy of exploration, and that's what scientists
[4:44] Speaker 1: been doing.
[4:45] Speaker 2: It's interesting you say that, and I'm thinking about how
[4:49] Speaker 2: so often parents actually have a better relationship with the
[4:54] Speaker 2: eldest child. Do they communication wise, they talk more, they
[5:00] Speaker 2: we spend more time together. Maybe that's joual like as
[5:03] Speaker 2: they get older.
[5:04] Speaker 1: I haven't seen any data on that, because researching favorites
[5:07] Speaker 1: is no.
[5:08] Speaker 2: But I don't think it's a favorite thing, like I honestly,
[5:11] Speaker 2: I don't think it's a favoritism.
[5:12] Speaker 1: Thing, just identifying the better relationship.
[5:15] Speaker 2: No, I think it's a direct result of spending more
[5:18] Speaker 2: time with that person.
[5:20] Speaker 1: So here's the second explanation, and this is what today's
[5:23] Speaker 1: doctor's desk is really all about. Brand new study in
[5:27] Speaker 1: American Economic Review tracked one point two million Danish kids
[5:32] Speaker 1: that were born since nineteen eighty. So this is a
[5:35] Speaker 1: big study, massive using government records, so we're.
[5:38] Speaker 2: Looking at so they haven't made anything up.
[5:41] Speaker 1: No, this is objective data. This isn't me saying, hey,
[5:43] Speaker 1: how do you feel subjectively? This is objective data. And
[5:46] Speaker 1: here's what they found. Respiratory infections in the first year
[5:50] Speaker 1: of life, so we talking about RSV. We actually had
[5:53] Speaker 1: some advertising from the government about RSV on the podcast
[5:56] Speaker 1: a little while ago, and we got bagged for it.
[5:58] Speaker 1: But the research on this is actually really really solid.
[6:00] Speaker 1: RSV and flu, mostly brought home by older siblings, predicted
[6:06] Speaker 1: lower earnings, less education, and worse mental health decades later.
[6:12] Speaker 1: So younger siblings were two to three times more likely
[6:14] Speaker 1: to be hospitalized with respiratory illnesses in year one. The
[6:19] Speaker 1: gap vanishes once both kids are in some kind of
[6:23] Speaker 1: drop care or daycare or early learning setting. So it
[6:27] Speaker 1: seems like the older sibling is the delivery system for illness,
[6:32] Speaker 1: and these researchers are suggesting that the birth order differences.
[6:38] Speaker 2: But the older child's still sick because they're carrying.
[6:41] Speaker 1: Right, But the older child has a much less compromised
[6:43] Speaker 1: immune system because they're older, they're stronger, they're more developed,
[6:46] Speaker 1: they're more capable, and so therefore they're less likely to
[6:49] Speaker 1: be negatively impacted by it. Let me go through a
[6:53] Speaker 1: couple of other things here. Early disease exposure explains half
[6:59] Speaker 1: or more of the entire birth order gap, maybe up
[7:03] Speaker 1: to seventy percent of the income gap, and then the
[7:07] Speaker 1: time with parents hypothesis probably explains the rest.
[7:12] Speaker 2: But if you're sick all the time, you would expect
[7:13] Speaker 2: you'd spend more time with moneth.
[7:15] Speaker 1: Well, yes, but and this is really important, but one
[7:21] Speaker 1: of the researchers identified that about eighty five percent of
[7:25] Speaker 1: a young infant's calories go to building the brain, and
[7:29] Speaker 1: if you have a serious infection, it's going to divert
[7:32] Speaker 1: those resources to fighting illnesses at exactly the moment when
[7:37] Speaker 1: those resources are supposed to be going to building the brain.
[7:40] Speaker 1: The first six months of life are specifically the most
[7:43] Speaker 1: critical window. Any significant exposure illness then is going to
[7:48] Speaker 1: do between two and three times the damage of exposure
[7:52] Speaker 1: in the second half of that child's first year. So
[7:56] Speaker 1: probably the last thing before we take a break and
[7:58] Speaker 1: then talk about what this means, and the question is
[8:00] Speaker 1: that it answers. I just want to reframe this briefly.
[8:05] Speaker 1: Small numbers, like maybe a one percent income dip, they're
[8:10] Speaker 1: going to hide a distribution where most kids are completely recovering,
[8:13] Speaker 1: and we're talking about population averages, So you get small
[8:17] Speaker 1: numbers and it's like, oh my goodness, what's happening here.
[8:20] Speaker 1: We're not saying that if you got sick in the
[8:21] Speaker 1: first year of life, that this is your destiny. What
[8:24] Speaker 1: we're highlighting is that the gaps that are appearing, it
[8:27] Speaker 1: seems like there's a credible hypothesis from this research that
[8:30] Speaker 1: it may actually be German illness related much more than
[8:33] Speaker 1: it's related to anything else that's going on in the house. Personality, temperament,
[8:38] Speaker 1: all that kind of stuff. So after the break, let's
[8:40] Speaker 1: answer some peak questions about the destiny associated with birth order.
[8:45] Speaker 1: Why do firstborn's win? We need to talk about that
[8:48] Speaker 1: and what we can do to protect our baby that
[8:50] Speaker 1: in a sect, say with back, it's the Happy Family's
[9:01] Speaker 1: podcast talking about birth order today.
[9:03] Speaker 2: Okay, so I'm just putting it out there. You make
[9:04] Speaker 2: me feel really bad as the firstborn. You're saying that
[9:07] Speaker 2: my siblings issues are a direct result of me bringing
[9:11] Speaker 2: germs home into the house as a young kid.
[9:14] Speaker 1: No, I'm not saying that at all.
[9:17] Speaker 2: I'm sure somebody's thinking it.
[9:19] Speaker 1: Well, maybe I'm saying it a little bit. So remember,
[9:21] Speaker 1: fifty to seventy percent is related to potentially that and
[9:25] Speaker 1: the other the rest of it is your parents' investment
[9:28] Speaker 1: in younger siblings.
[9:29] Speaker 2: We have one granddaughter, and she has made all of
[9:32] Speaker 2: us sick multiple times.
[9:36] Speaker 1: Here's what I want you to know. Birth order is
[9:38] Speaker 1: not the destiny, not like where you're born in the family,
[9:41] Speaker 1: that that's the headline, but the two main drivers.
[9:44] Speaker 2: So just don't have a firstborn that man.
[9:48] Speaker 1: Just have later born.
[9:51] Speaker 2: Okay, let's get a bit serious. I know I'm hijacking
[9:53] Speaker 2: your whole your whole podcast here. What can we do
[9:57] Speaker 2: about this when it would seem that our younger children
[10:02] Speaker 2: are actually at a disadvantage, but you are suggesting that
[10:05] Speaker 2: maybe not.
[10:05] Speaker 1: Well, I think younger children technically have the advantage older parents,
[10:09] Speaker 1: more economic resources, all that sort of stuff. But firstborns
[10:12] Speaker 1: are consistently winning. So then the firstbornes, even though parents
[10:16] Speaker 1: are usually less wealthy, less experienced, less likely to really
[10:22] Speaker 1: be there. The data says none of it out weighs
[10:25] Speaker 1: three thousand lost hours and a first year immune system
[10:28] Speaker 1: that's under siege. I think that that's really what we're
[10:30] Speaker 1: getting at here, all of those extra hours that the
[10:33] Speaker 1: kids are not getting with their parents, three thousand hours
[10:36] Speaker 1: of reading and playing, and that's huge, and that first
[10:39] Speaker 1: year immune system situation, that's that's the thing.
[10:42] Speaker 2: So we bubble our firstborn children up until our second
[10:48] Speaker 2: and subsequent babies are a year old.
[10:50] Speaker 1: Is that what we're That's kind of what it sounds like.
[10:53] Speaker 2: I have to I have to wrap my head around this.
[10:55] Speaker 1: Yeah, yeah, that's kind of what it sounds like.
[10:57] Speaker 2: So the idea, So I have noticed with this generation
[11:01] Speaker 2: of parents that mums are very reluctant to hand over
[11:07] Speaker 2: brand new babies. They don't like other people kissing them
[11:11] Speaker 2: or wrapping them up and you know, giving them big
[11:13] Speaker 2: cuddles and things. And this research would actually support that. Yeah.
[11:19] Speaker 1: The researchers make for suggestions number one immunizations on schedule
[11:23] Speaker 1: that includes RSV flu hooping, CoV vaccinations, and pregnancy because
[11:28] Speaker 1: that is going to give you protection for your newborn
[11:31] Speaker 1: breastfeeding if you can. I know that there's a lot
[11:33] Speaker 1: of questions around this. Not everyone can do all these things,
[11:35] Speaker 1: but breastfeeding is massively, massively protective. In the Danish study,
[11:40] Speaker 1: it was so powerful. They said that sustained breastfeeding eliminated
[11:45] Speaker 1: the excess hospitalization risk for high exposure younger siblings entirely.
[11:51] Speaker 1: And they also recommend this one's going to sound so boring, hello,
[11:54] Speaker 1: COVID boring old hygiene wash hands, especially when the kids
[12:00] Speaker 1: come home daycare clothes off. Six siblings have to be
[12:03] Speaker 1: kept away from the newborn, especially in those first six
[12:06] Speaker 1: months of life. That's kind of it.
[12:08] Speaker 2: Well, I guess the great news is that all of
[12:10] Speaker 2: those things are completely doable. Any parent can tackle those
[12:14] Speaker 2: three things. But I am curious about the time difference
[12:20] Speaker 2: deficit between the elders getting so many more hours investment
[12:26] Speaker 2: from a parent compared to younger children.
[12:28] Speaker 1: I said four things, and I said three because they
[12:29] Speaker 1: were related to health. The fourth thing is trying to
[12:32] Speaker 1: be fair in terms of your allocation of time. The
[12:36] Speaker 1: more time you can give you young kids, the better.
[12:38] Speaker 1: But I think we've got to recognize the constraints around that,
[12:40] Speaker 1: so being fair across time. Like our youngest now, she's
[12:45] Speaker 1: one of only a couple of kids at home requiring
[12:47] Speaker 1: time of so she's getting probably more time than any
[12:50] Speaker 1: of the other kids I've ever had, But she didn't
[12:52] Speaker 1: get nearly as much time when she was younger. So
[12:54] Speaker 1: we're trying to trying to pull it all together. You
[12:58] Speaker 1: know what, family life life could be really really tricky.
[13:01] Speaker 2: I think if you sit there with a scorebook and
[13:03] Speaker 2: you try and make sure that you're allocating equal time
[13:07] Speaker 2: and resources to each child, You're going to drive yourself
[13:11] Speaker 2: insane and it's going to be less productive. I think
[13:15] Speaker 2: the most important thing is just trying to be available
[13:17] Speaker 2: for your children when they need you and allocating special
[13:22] Speaker 2: one on one time.
[13:24] Speaker 1: That's about it. Your youngest child is not doomed, your
[13:26] Speaker 1: eldest is not blessed, but the invisible defaults of family
[13:31] Speaker 1: life are probably going to tilt the table towards your
[13:34] Speaker 1: eldest and the resource that they can get access to. Really,
[13:38] Speaker 1: what this evidence says is vaccinate, breastfeed, if you can
[13:42] Speaker 1: wash the big kids hands and read to your youngest
[13:45] Speaker 1: as if she's your eldest is if she's your first one.
[13:48] Speaker 1: It seems like the birth order effect is real, but
[13:52] Speaker 1: we have a lot of it in control. Like Kylie said,
[13:54] Speaker 1: we're back tomorrow with older, but it tomorrow. Thanks so
[13:56] Speaker 1: much for joining us for this conversation. Love to know
[13:58] Speaker 1: what you think. Jump onto our social and tell us
[14:01] Speaker 1: that Family's podcast audio and sound justin rule on Bridge
[14:04] Speaker 1: Media admin and other support from Mim Hammond's If you'd
[14:08] Speaker 1: like more of her to make your family happier, you'll
[14:09] Speaker 1: find it at happyfamilies dot com, dou

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