Granite Hill Campground has it's own mini-golf that's open to the public. Probably OK for the 5 year old but not sure on the toddler. Boyd's Bear Factory closed, so that's not an option. Try this link:
http://www.gettysburg.travel/visitor/do.asp. The animal park in Maryland is only 30 minutes away. It's been a while since I've been there but I remember it being fairly well done. I think the kids can get pony rides at Artillery Ridge campground. My suggestion would be to pick a campground that has a pool and a playground, wear the kid out, then tour the battlefields while they sleep! :B Hershey Park is only about an hour away, so that's an option but it will probably eat a whole day.