Inis Grove Park in Ames has a new playground called the Barnes Family Inclusive Playground. There are several different play areas, which are great for little kids and big kids. The City of Ames map below shows a great overview.
There are parking lots on both the west and east sides of the playground, and restrooms near both parking lots as well. The east restrooms are a little more conveniently located, as they're just past the swings.
UPDATE: The playground below has been replaced with a new playground.
Behind the trees at Inis Grove Park are hiking trails and another older playground.