Background: Identifying factors influencing the implementation of evidence-based environmental recommendations to promote physical activity in childcare services is required to develop effective implementation strategies. This systematic review aimed to: (1) identify barriers and facilitators reported by center-based childcare services impacting the implementation of environmental recommendations to increase physical activity among children, (2) synthesize these factors according to the 14 domains of the “Theoretical Domains Framework,” and (3) report any associations between service or provider characteristics and the reported implementation of such recommendations. Methods: Electronic searches were conducted in 6 scientific databases (eg, MEDLINE) and Google Scholar to identify studies reporting data from childcare staff or other stakeholders responsible for childcare operations. Included studies were based on childcare settings and published in English. From 2164 identified citations, 19 articles met the inclusion criteria (11 qualitative, 4 quantitative, and 4 mixed methods). Results: Across all articles, the majority of factors impacting implementation fell into the “environmental context and resources” domain (eg, time, equipment, and space; n = 19) and the “social influences” domain (eg, support from parents, colleagues, supervisors; n = 11). Conclusion: The current review provides guidance to improve the implementation of environmental recommendations in childcare services by addressing environmental, resource, and social barriers.