Background: Dog ownership is a catalyst for physical activity in adults. Given 50-70% of Australian households with children have a dog, dog-facilitated physical activity may be an effective way to increase physical activity and decrease child obesity. Objective: We hypothesized that children with a family dog walk more, are more physically active and are more likely to achieve recommended levels of weekly physical activity compared with children who do not have a dog. Method: Cross-sectional data from the Western Australian TRravel, Environment, and Kids project (TREK) were analyzed for 1218 children aged 10-12 years. Individual and environment factors, child physical activity, walking, screen use, sedentary behaviour and dog ownership status was collected from child and parent questionnaires. Children's height and weight were measured. Results: Approximately 60% of children had a family dog. Dog ownership was associated with, on average, 29 more minutes of walking and 142 more minutes of physical activity per week (P ≤ 0.01). After adjustment, children with a dog were 49% more likely to achieve the recommended level of weekly physical activity (420 min) and 32% more likely to have walked in their neighbourhood in the last week, compared with non-dog owners (P ≤ 0.05). These relationships varied by gender. Dog ownership was not associated with screen use or weight status. Conclusions: Dog ownership was associated with walking and physical activity, but not screen use or weight status. Within dog-owning families, the promotion of walking and active play with a dog may be a strategy to increase children's physical activity.