Turtle Park DC Playground
The closest to the entrance on Van Ness St NW is a little kids' playground that is fully fenced in and nicely shaded at almost all times of day. It has plenty of equipment for every style of play, including slides, swings, a sand pit, and a few misfit toys like play kitchens and ride-on trucks to share.
Despite being a very popular playground, it somehow never feels crowded. The big kids' playground is across from Friendship Recreation Center, and includes slides, swings, and a very cool climbing structure, but is not shaded and can get hot. Beyond the playgrounds are basketball courts, tennis courts, and fields for running around.
Check out more DC Playgrounds here.
The splash pad is in the foreground. More info on all DC Splashpads here.