Objective To examine associations between active play and the physical activity of 10- to 11-year-old children. Method Cross-sectional study of 747, 10- tot11-year-olds, conducted between February 2008 and March 2009 in Bristol, UK. Mean minutes of moderate to vigorous physical activity (MVPA) and mean activity levels (counts per minute, CPM) were assessed by accelerometer. Frequency of active play was self-reported. Results Regression models indicated that frequent active play (5 or more days per week) was associated with mean daily activity levels (CPM) (girls: p = < 0.01; boys: p = <0.01), but was only associated with mean daily MVPA for girls (p = < 0.01). For leisure-time physical activity, active play was associated with children’s CPM (girls: p = 0.02; boys: p = < 0.01) and MVPA (girls: p = < 0.01; boys: p = 0.03) on weekdays after school, but was only associated with weekend day CPM for boys (p =<0.01). Conclusion Active play is associated with children’s physical activity with after-school potentially being a critical period. Strategies to promote active play may prove to be a successful means of increasing children’s physical activity.