AbstractAimsTo investigate associations between outdoor and screen time and changes in sleep patterns in children from two nationwide birth‐cohorts in the SAPRIS project.MethodsDuring the first French COVID‐19 pandemic lockdown, volunteer parents of children enrolled in the ELFE and EPIPAGE2 birth‐cohorts completed online questions about their child's outdoor time, screen time, and changes in sleep duration and quality compared with the pre‐lockdown situation. In 5700 children (aged 8–9 years, 52% boys) with available data, we assessed associations between outdoor time, screen time, and sleep changes using multinomial logistic regression models adjusted for confounders.ResultsChildren spent on average 3 h08 outdoors and 4 h34 using screens/day (3 h27 for leisure, 1 h07 for class‐work). Sleep duration increased in 36% of children and decreased in 13.4%; sleep difficulties appeared/increased in 22.5% and decreased/disappeared/remained stable in 18.3%. After adjustment, increased screen time, especially for leisure, was associated with increased and decreased sleep duration (OR(95%CI) = 1.03(1.00–1.06) and OR = 1.06(1.02–1.10), respectively). No association was observed between outdoor time and sleep changes after adjustment.ConclusionsOur study adds evidence for the association between high leisure‐time screen time and shorter sleep time. It supports current screen guidelines for children, especially during leisure time and for those whose sleep duration is short.