Physical activity may protect against overweight and obesity among preschoolers, and the policies and characteristics of group child care centers influence the physical activity levels of children who attend them. We examined whether children in New York City group child care centers that are compliant with the city's regulations on child physical activity engage in more activity than children in centers who do not comply. Methods A sample of 1,352 children (mean age, 3.39 years) served by 110 group child care centers in low-income neighborhoods participated. Children's anthropometric data were collected and accelerometers were used to measure duration and intensity of physical activity. Multilevel generalized linear regression modeling techniques were used to assess the effect of center- and child-level factors on child-level physical activity. Results Centers' compliance with the regulation of obtaining at least 60 minutes of total physical activity per day was positively associated with children's levels of moderate to vigorous physical activity (MVPA); compliance with the regulation of obtaining at least 30 minutes of structured activity was not associated with increased levels of MVPA. Children in centers with a dedicated outdoor play space available also spent more time in MVPA. Boys spent more time in MVPA than girls, and non-Hispanic black children spent more time in MVPA than Hispanic children. Conclusion To increase children's level of MVPA in child care, both time and type of activity should be considered. Further examination of the role of play space availability and its effect on opportunities for engaging in physical activity is needed. (author abstract)