We examined the relationship between physical activity parenting (PAP) and child, family, and environmental factors in families. The participants were 840 families with young children (n=993; 5.40±1.14years) and parents (n=993; 35.8±5.29years). Parents' self-reported PAP (co-participation, (in)direct support, and encouragement), child-specific (sex, age, temperament, outdoor time, organized physical activity or sports, sedentary time, media time, PA enjoyment, motor skills compared to peers, PA, and sport facility use), family-specific (respondent's sex, age, education, exercise frequency, family income, family status, number of children in the family, child's birth order and partner's PAP, and exercise frequency), and environment-specific (residential density, access to sport and outdoor facilities, type of house, and access to electronic devices) factors were collected. Children's motor skills and anthropometrics were measured. After adjusting for the family cluster effect, child, family, and environmental factors were entered into a linear mixed-effects model, with PAP as the response variable. The final model consisted of statistically significant factors, and parental education, which was forced into the model. Nine child- and family-related factors explained 15% of parenting variance between the children and 52% between the families. Partner's PAP (B=0.68, P<0.001) had the strongest association, whereas the child's temperament (B=0.08, P<0.001) and birth order (B=-0.10, P<0.001) had smaller but novel associations with the respondent's PAP. Partner's PAP and a range of child- and family-related factors should be considered when promoting parental support for child PA.