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.