Ohio, Indiana & Kentucky Camp Suggestions

Cedar point is one obvious possibility. They have a (seemingly very nice) RV park right on the property. It isn't inexpensive, but going to an amusement park with on-site camping has lots of advantages that are hard to get otherwise. You can run back to take an afternoon nap, for example, or eat a good supper made yourself rather than waiting in like and partaking of fairground food.

Another decent idea is Mammoth Cave. I remember thoroughly enjoying it (and most other caves, really) as a youth...and I don't believe that would have changed in the years since then.