Background: Although more than 1 million US children attend licensed family child care homes, little is known about children's physical activity in this setting. The purpose of this study is to describe the physical activity of children cared for in child care homes. Methods: The study sample included 31 licensed family child care homes in Washington State. Children aged 3 to 6 wore accelerometers while in child care over 5 days. Minutes per hour spent at 4 activity levels were calculated and averaged for all children in the home. Contextual factors such as provider practices, staff training, and home characteristics were assessed using standardized questions. Results: Accelerometer data from 144 children were included, with 2 to 11 children monitored per home. The mean minutes of sedentary activity per hour (min/h) was 34.3 (SD = 4.6, range 27.7 to 46.6). For moderate-to-vigorous activity (MVPA) it was 8.8 min/h (SD = 2.6, range 3.6 to 14.1) and for vigorous physical (VPA) activity it was 3.1 min/h (SD = 1.4, range: 0.9 to 7.0). Conclusions: The low levels of MVPA and VPA in many homes reinforces the need for additional research to identify policy and practice recommendations that will be most effective in increasing physical activity in this setting. (author abstract)