Objectives: The aim of this study was to simultaneously explore multiple pathways through which sports participation during childhood and adolescence may be associated with adiposity over time. Design: Data were drawn from the Kindergarten cohort of the Longitudinal Study of Australian Children. A total of 4286 children provided sports participation data at age 10 years and were followed up 24 and 48 months later. Method: Time spent in organised sports at age 10 years and time spent in physical activity at age 12 years were measured via parental-reported time-use diary. Dietary behaviours were self-reported at age 12 years. Screen time was parent-reported. Body fat was measured at age 14 using bioelectrical impedance analysis. Two parallel multiple mediation models were tested to examine the longitudinal associations between sport participation at age 10 and body fat at age 14 via the mediating variables of physical activity, screen time, and dietary behaviours. One model was run for all participants, and a second model was run only for those participants who reported participating in organised sports. Results: There were no significant indirect relationships between sports participation and body fat via any of the mediating variables in the total sample, or among sport participants. Conclusions: There is a dearth of evidence to support substantial rhetoric and policy to promote organised sports programs as public health initiatives in their current form during childhood and adolescence. Better quality evidence is needed, however, modifications to sport programs may be necessary to elucidate meaningful benefits for adiposity.