This study examined sex differences in child friendship networks relative to summer care programs and associations with self-reported physical activity (PA) across summer. Children (n=182; mean age = 9.93 years; SD = 1.28) at two summer care programs reported PA and information about up to five people they hung around with at the program and five outside the program at the beginning and end of summer. Male children reported significantly more PA than females at both timepoints. Average PA of in-program friends was significantly associated with PA for both sexes. More studies should acknowledge access to summer care programming when assessing summertime PA.