BackgroundThere are two alternative mechanisms, elucidating the reciprocal relationship between self-efficacy and social support when explaining health outcomes: self-efficacy beliefs may operate as the establisher of social support (the cultivation model) or social support may enable the formation of self-efficacy beliefs (the enabling model).PurposeIn line with the cultivation hypothesis, it was tested if self-efficacy (measured in parents and children) would indirectly predict parental and child moderate-to-vigorous physical activity (MVPA), via the mediator, social support (parent-provided, child-received). In line with the enabling hypothesis, it was tested if social support would predict MVPA indirectly, via the mediator, self-efficacy. MethodsA total of 879 parent–child dyads (1758 individuals; 52.4% girls, aged 5–11 years old, 83.2% mothers) provided self-reports at the baseline (T1) and the 7- to 8-month follow-up (T2). Body weight and height were measured objectively. Manifest path analyses were performed, controlling for the baseline levels of the mediator and dependent variables.ResultsA similar number of significant simple indirect effects was found for the cultivation and the enabling model. Across the models, the indirect effects followed similar patterns: (a) within-individual indirect effects in children; (b) across-individual indirect effects, with the independent variable measured in children and the mediator/dependent variables measured in parents (e.g., child self-efficacy predicted parental support provision and, indirectly, parental MVPA); (c) across-individual indirect effects, accounting for self-efficacy and MVPA measured in children, combined with parental reports of social support.ConclusionsThe findings provide support for both cultivation and enabling models in the context of MVPA among parent–child dyads.