This study investigated children's after-school activity and associations with body mass index (BMI) and family circumstance. One thousand two hundred thirty-four parents and 854 children (age 8-13 years) completed activity diaries for the 2 hours after school. Parents reported children as more active than children reported themselves. Boys were reported to be more active than girls. Activity levels were generally not associated with BMI or family circumstance with the exception of cultural background. Parent-reported mean child METs were higher for mothers born in Australia (3.3 vs. 3.0; p = .02). Child-reported mean METs were higher for fathers born in Australia (2.9 vs. 2.6; p = .04) and where english was their main language (2.9 vs. 2.3, p = .003).