McHenry Park in Des Moines has a splash pad and natural playscape. Hours for the splash pad are 9 am to 8 pm. There's no parking lot, but street parking is easy to find and restrooms are near the shelter by the splash pad.
As you walk south from the playscape, you'll see a great view of Riverview Park which is just down the hill. It's connected by trail and has a new playground.
We were at McHenry Park this morning for Des Moines Public Library outdoor storytime. It was a fun mix of books, songs, a craft and parachute play.