Take your family to Knobels Grove.
Free admission, free parking you can bring snacks, although the food is reasonable and you can pay per ride with tickets that never expire or get a ride band. They also have a wonderful spring fed pool.

DO NOT waste the the money taking an infant and 4 year old to HP. You’ll be paying almost $200 to get in even if the kids are free. To do what? You won’t be able to ride rides together.
Save HP for when the kids are older.