The $30 million study on sibling dynamics

A team of researchers from Monash University has conducted a comprehensive study on the impact of birth order on parenting styles and childhod experiences, analyzing data from 5,000 children aged two to 15 years old.

The study, published in the Journal of Economic Behavior & Organisation, found that parents impose fewer rules on younger siblings, resulting in nine to 14 extra minutes of screen time daily.

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The findings align with previous studies on birth order and parenting styles, which suggest that parents become more lenient with rules for later-born children when they are older, corresponding with older later-born children spending more time with digital media.

The researchers also discovered that among second-born girls, the gender of their older sibling can have an effect on the expectations parents place on them, with a reduction in the perceived expectation to follow family rules when their older sibling is also a girl.

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The study suggests that the increase in digital media time for later-born children is largely driven by those activities that children do alone, with parents less likely to have rules around TV watching and video games for later-born children.

The researchers grouped all activities into seven categories: sleep, school, enrichment activities, physical activities, social activities, digital media, and general care, with digital media including television, video games, internet use , and social media.

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The study found that compared with first-born children, second and third-borns spend between nine and 14 minutes extra each day looking at screens, with the researchers stating that their results are consistent with a previous study that found later-born children are less likely to experience strict parental supervision regarding homework and rules on watching TV.

The team also referenced a separate 2017 brain study from Southwest University in Chongqing, China,which found that only children have different brain structures that correlate with higher creativity but lower agreeableness, potentially making them more self-focused and less empathetic.

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The Monash research provides empirical evidence for longstanding cultural observations about sibling differences , while the Chinese study opens a window into the neurological implications of being an only child, highlighting the complex interplay between genetics, environment, and parenting in shaping who we become.

The findings offer a scientific lens on family dynamics that many will recognize from their own childhood experiences , with the study suggesting that future research may explore the long-term outcomes of these early differences in screen time and social development, or investigate how parental leniency might affect academic achievement and mental health across the lifespan.