Splash pads in Upper Marlboro, Maryland

Watkins Regional Park is Prince George's County's full-day destination — train, mini-golf, carousel, nature center, AND a large free spray park that's the centerpiece for hundreds of families on summer Saturdays. Free parking is plentiful (lots fill by 11am on weekends). Restrooms throughout the park. Best on weekday mornings if you can swing it — the spray park gets genuinely packed on weekends, but the train and mini-golf absorb the overflow. Operates Memorial Day through Labor Day. Bring lunch — picnic pavilions are free first-come, and the food options on-site are basic. PG County humidity is brutal in July; morning visits dodge afternoon thunderstorms. The most complete free family day in the DMV.