Participation in school sport teams and self-efficacy was positively associated with PA in boys. Girls who reported participation in school sport teams, who perceived more peer support, had a more supportive home PA environment, and spent more time doing homework were more physically active. Family support for PA was negatively and homework was positively, associated with boys’ SBBs. Body mass index and parent role modeling of TV was positively associated with TV viewing, whilst more sedentary opportunities in the home were associated with higher Internet use/e-games playing among girls.