The purpose of this study is to design, implement, and evaluate a recreation site-based obesity prevention and control intervention for 7-9 year old children and their families by targeting physical activity and dietary behaviors. The intervention will target the home as well as community environment (specifically urban recreation centers; but also, other aspects of the neighborhood). This study will produce innovations in obesity interventions and the understanding of mediators of change. Recreationcenters are an important public resource whose contribution to physical activity promotion is unknown but has the potential to be significant. The primary aim is to evaluate the effectiveness of a multi-level intervention to prevent the onset of overweight and obesity in 7-9 year old children. The recreation center site intervention emphasizes changes in quantity and quality of physical activity and nutrition-related offerings within the centers. The home site intervention will target the home and household rule setting delivered via recreation center-based community health advisors and tailored to the needs of the family. Community health advisors will work in home and neighborhood environments to advocate environmental change. Secondary research aims include: 1. To modify the setting and enforcement of rules and to establish home environmental controls of childhood nutrition and physical activity behaviors; and to assess the extent to which changes in these mediators lead to changes in proximal outcomes (physical activity, sedentary behavior, and nutrition). 2. To determine and attempt to modify patterns of setting and enforcement of rules and home environmental control of childhood nutrition and physical activity, and to assess the extent to which changes in these mediators lead to changes in proximal outcomes (physical activity, sedentary behavior, and nutrition). 3. To determine mediators (barriers and facilitators) of healthy and unhealthy eating and physical activity/sedentary behavior in recreation centers, and to assess the extent to which changes in these mediators lead to changes in proximal outcomes (physical activity, sedentary behavior, and nutrition). 4. To develop and apply observational measures of physical activity and dietary behaviors (adapted from SOPLAY) appropriate for recreation centers and parks. 5. To assess the impact of hypothesized intervention moderator variables (e.g., race/ethnicity, demographics, acculturation, immutable environmental factors) on behavioral and weight outcomes.