The study draws on data from 1,668 children, 849 boys and 819 girls, enrolled in the Quebec Longitudinal Study of Child Development (QLSCD), a population-based cohort of children born in 1997-98 and coordinated by the Institut de la statistique du Québec.
At age 2.5, parents reported how often they engaged in active leisure with their child, how much time the child spent in front of screens each day (television, video, computers and video games) and how long the child slept on average, naps included. Those same children were then surveyed at age 12 about their outdoor play habits and physical activity levels during leisure time.
To rule out alternative explanations, the researchers controlled for a wide range of factors that could influence the results: the child's temperament, body mass index and neurocognitive abilities, as well as maternal depressive symptoms, education level, family structure and household income, among others. Analyses were conducted separately for boys and girls to account for their distinct developmental trajectories.
What sets this study apart
The question of whether early childhood habits predict adolescent lifestyle is not new. But the scientific evidence, until now, has been thin. Most previous studies offered only a snapshot in time, without following children over the long term.
What distinguishes this research is the strength of its case: a representative population cohort, more than ten years of follow-up, rigorous controls for individual and family factors, and sex-specific analysis. Together, these elements make it possible, for the first time, to say with confidence that movement habits formed at age 2.5 have measurable ripple effects a decade down the road.
Habits that hold ten years on
The results are striking. Children who played actively with a parent every day, or who spent fewer than an hour in front of a screen, were significantly more physically active at the start of adolescence.
Concretely, each additional "good" movement habit at age 2.5 was associated with roughly five more minutes of outdoor play per day at age 12, for both boys and girls. Among girls, active play, limited screen time and adequate sleep at two and a half were also linked to higher levels of leisure-time physical activity at greater intensity and frequency.
These associations held up even after accounting for all pre-existing individual and family factors, which substantially strengthens the findings.
"Active parent-child time - playing, moving, being physically engaged together - appears to be the single most powerful lever for establishing healthy long-term habits," said Harandian. "Those shared experiences help children associate movement with enjoyment, motivation and routine."
Girls in early adolescence: a window of particular vulnerability
The findings also illuminate a troubling reality: at adolescence, girls are especially at risk of becoming sedentary. By age 12, only 14.9 per cent of girls in the cohort were considered active in their leisure time, compared with 24.5 per cent of boys. By limiting their daughter's screen time early and engaging actively in her play, parents appear to lower the barriers to an active lifestyle, and plant the seeds of lasting physical engagement.
