Twin Grove has lots of amenities for the kids, but if you get a site on the side of the hill and it is hot, you'll bake. If you are camping the week of July 13th, I'd skip Twin Grove. Both the East Coast Xterra Challenge and Coal Mine Cruiser Classic are that week at Rausch Creek Off-Road Park. Both events use Twin Grove for camping.
Jonestown really doesn't have any amenities, other than the creek, but it is a much more shady campground.
Hershey High Meadow Campground is nice. The pull through section is a little snug though. There's a bunch of stuff to see and do around Hershey (aside from the park) as well as your other site seeing plans.
-Michael