The numbers are sobering: nearly 80 per cent of the world's teenagers don't get enough physical activity, according to the World Health Organization. But a new longitudinal study from Université de Montréal suggests the seeds of that sedentary lifestyle — or an active one — may be sown much earlier than anyone realized. Like when a child is two and a half years old.
Led by doctoral researcher Kianoush Harandian and UdeM psycho-education professor Linda S. Pagani, in collaboration with internationally recognized physical activity expert Dr. Mark Tremblay of the University of Ottawa, the study finds that three simple movement habits in toddlerhood — active play with parents, limited screen time and sufficient sleep — significantly predict a more physically active lifestyle a full decade later.
"When we analyzed the data, we found that fewer than one child in ten naturally met all three daily movement recommendations: active play, limited screens and enough sleep," said Harandian. "And yet these early habits matter enormously. They lay the foundation for how children will choose to spend their time as adolescents."
Nearly 1,700 children, followed for over a decade
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.
A clear message for families and policymakers
"Family habits breed individual habits across a child's entire development," said Pagani. "By encouraging active play, setting boundaries around screens and prioritizing quality sleep from the earliest years, parents exert a durable, measurable influence on their children's long-term well-being."
The study calls for broader dissemination of WHO guidelines for children under five — at least 180 minutes of physical activity per day, no more than one hour of sedentary screen time, and 11 to 14 hours of sleep — and makes the case for hospitals, schools and public health organizations to target family lifestyle habits from the very start.
About the study
" Active Parent–Child Leisure, Sedentariness, and Sleep in Toddlerhood Promise Later Active Lifestyle in Early Adolescence ", by Kianoush Harandian and collaborators, was published [DATE] in the Journal of Developmental & Behavioral Pediatrics. Lead author Kianoush Harandian is affiliated with the School of Psycho-Education at Université de Montréal. Co-authors are Laurie-Anne Kosak (Université de Sherbrooke), Mark Tremblay (University of Ottawa; CHEO Research Institute) and Linda S. Pagani (Université de Montréal). The study was supported by the Social Sciences and Humanities Research Council of Canada and Sport Canada.
