This paper describes the development and evaluation of a Park Prescription (DC Park Rx) program for low-income residents in Washington, DC which aims to increase the amount of physical activity in children and adolescents who are at risk for chronic illness. The findings indicated that behaviours and attitudes relating to health and physical activity can change through a park prescription program. The number of days per month spent in a park for 30 or more minutes increased from 7 to 8 days, and the average weekly physical activity increased from 150 to 172 minutes. Additionally, more parents believed that physical activity was important for the health of their child and made physical activity a regular focus for their family. Responses on both the pre- and post-surveys indicated that parents considered the parks to be safe and that they valued parks as places to be physically active and to enjoy nature.