If you've got young kids and find yourself about 100 miles into PA (from the East), check into Knoebel's Amusement Park in Elysburg, not far from Danville (exit 224 on I-80).
Parking and entrance is free; pay by the ride, although they offer all-you-can-ride passes.
Lovely park with lots of benches and shade, lots of good rides, especially for little ones, cheap, decent food, big swimming pool, slide, etc.
We had a blast with our almost 5 year old GS. Lots of rides for older kids and adults, too.
(My only connection with Knoebel's is as a customer.)