This systematic review aimed to explore the influence of family factors on physical activity in children with intellectual disability. How and what family factors that specifically influence physical activity has not been compiled and reviewed previously. In accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a systematic search was performed for articles published in English and Chinese without any year limits in six databases. Ten studies met the eligibility criteria and were included in the review. All studies were qualitatively integrated to identify and compare positive and negative family factors. A total of 1135 participants, of which 497 were children with intellectual disability while the other 638 participants were family members (parents, siblings and caregivers). The family factors of 6 themes and 18 sub-themes (10 positive, 7 negative and 1 inconclusive factors) were extracted. Overall, these results highlight the importance of encouragement, support and involvement by family members, concurrently it points out that parental psychological factors, socioeconomic status, responsibilities and electronic devices could both promote and hinder engagement in physical activity for children with intellectual disability. The findings accentuate the role of the family unit in helping determine the activity levels of children with intellectual disability. Future studies should include a wider range of participants and be longitudinal in nature, utilizing more accurate monitoring tools.