There are several fun playgrounds in the area.
The Outflow Campground playground, Confluence. This is across the river from the Treehouse and Riverhouse. Walk or bike across the Yough River bridge (281) and head towards the end of the campground. There is a great spot for fishing there as well, at the outflow of the dam.
The Turkeyfoot school playground, Harnedsville. Unknown, this is great spot when school is out.
Stewart On The Green Community Park, Ohiopyle. Newer and cool playground with kayaks built into the structures.
The Confluence community playground, Confluence. Not great but cool if your kiddos like to watch the train go by. Next to the Community center (near Foodmart)