Physical activity (PA) participation is prone to decline during childhood and adolescence. In Australia, this decline has been shown to particularly occur in active play. This study aimed to identify sociodemographic moderators of change in active play between 10-11y and 12-13y among Australian youth. The data were sourced from Waves 6-7 of the Longitudinal Study of Australian Children ( = 3567). Active play participation was measured using one-day time-use diaries (TUDs) completed by youth. Potential sociodemographic moderators were tested using multilevel mixed modelling, adjusted for pubertal development, body mass index z-score and TUD contextual variables (school attendance and season). Active play declined more among girls (β= -7.6 min/day, 95% CI = -13.3, -1.8), those who spoke English at home (β= -12.3 min/day, 95% CI = -22.0, -2.7) and marginally among those in regional/remote areas (β= -6.3 min/day, 95% CI = -12.8, +0.1). A widening gap in active play by sex was observed, while differences by language spoken at home and geographical remoteness weakened or became marginal over time. Interventions to promote active play could target girls in the transition to adolescence. Future studies could investigate whether active play declines earlier than 10-11y among youth who speak languages other than English at home and those living in urban areas.