Y.L.
My sister threw a party for her 4 year old son at Chick-Fillet. She made sure they had a play area for the kids. The stuff were great. They even dressed up as a cow. They didn't charge her for using part of the restaurant but the play area was shared with other kids too. She just had to buy food and drinks there.
There is also the Smith Playhouse in Fairmount Park. They do charge but there is plenty of room for activities and different places for the kids to play.
Have Fun.