Adapted from BMJ 18-25 April 2026
Firstborn children are known to outperform their later born siblings in adulthood regarding earning capacity and IQ. It has now been shown that these differences start really early in babyhood from research published in JAMA.
In Japan, 2,000 sibling pairs were tested regarding cognitive skills and developmental milestones. By six months of age, the older siblings outperformed the younger ones. Some of the differences evened out by the age of 12 months, but deficits in fine motor skills and personal-social areas persisted.
This difference however is paralleled by lower parental engagement for second born and subsequent children. Resources become diluted as families grow.
My comment: I do remember slacking off with my second son compared to my first. The first one got everything done by my Penelope Leitch book.
The second got warmer and more social baths, far fewer photographs taken, was able to decide his own bedtimes, decided when he was ready to get toilet trained, I found him trying to change his own nappy, and I didn’t bother trying to get him to eat vegetables or anything he didn’t immediately like. He also stayed on bottled milk far longer. He was able to get these himself out of the fridge. Unlike baby #1 I didn’t warm up the milk after one month of age and he took it chilled.
I hope my lack of diligence in one side of the equation gave me more time to spend talking to him and playing with him on the other. He did speak far later though.
They have both done very well in adulthood although the limited dietary intake persists. I do think the younger child had a better time of it with a more relaxed parenting style.
Diabetes Diet 