Background: Opportunities for physical activity within out of school hours care (OSHC) are not well documented in Australia. This study explored factors associated with children (5–12 years) meeting 30 min of moderate to vigorous physical activity (MVPA) while attending OSHC in the afternoon period. Methods: A cross-sectional study, conducted in 89 OSHC services in New South Wales, Australia, serving 4,408 children. Each service was visited twice between 2018–2019. Physical activity promotion practices were captured via short interviews and System for Observing Staff Promotion of Physical Activity and Nutrition (SOSPAN). Physical activity spaces was measured (m2) and physical activity of 3,614 child days (42% girls), were collected using Acti-Graph accelerometers. Association between program practices and children accumulation of MVPA was tested using mixed effects logistic regression, adjusted by OSHC service and child. Results: Twenty-six percent of children (n = 925) accumulated 30 min or more of MVPA. Factors associated with children reaching MVPA recommendations included: services scheduling greater amounts of child-led free play, both 30–59 min (OR 2.6, 95%CI 1.70, 3.98) and ≥ 60 min (OR 6.4, 95%CI 3.90, 10.49); opportunities for staff-led organised play of ≥ 30 min (OR 2.3, 95%CI 1.47, 3.83); and active games that engaged the majority of children (OR 1.7, 95%CI 1.11, 2.61). Children were less likely to meet MVPA recommendations if services played games with elimination components (OR 0.56, 95%CI 0.37, 0.86). Conclusion: Improvements to service-level physical activity promotion practices, specifically the type of physical activity scheduled and the structure of games, may be an effective strategy to increase MVPA of children attending OSHC afterschool in NSW, Australia.