N.K.
HI--I hope you get answers, b/c I'd like to know too.
There's Giggleberry Fair in Lahaska/New Hope at Peddler's Village (google it, they have a website). It's not free, but they have games and a carousel. The indoor jungle gym is more for kids older than yours.
In Philly there's Please Touch Museum and Franklin Institute.
In New Hope, there's a historic train ride, but it's way overpriced. It's fun though.
There is a playground in Lambertville, near the Moustache restaurant and the canal. I can't remember the street--I think it's at Union and something. It's a small one, but cute and there's usually kids there.
Hope this helps? Maybe you could post back with the places you already know.
thanks, N.