Welcome to my neck of the woods!
We have been to both Holiday World and Mammoth Cave a BUNCH.
First of all - please know that Holiday World is definitely NOT WDW. But you probably already know that. The rides do not accomodate Pooh sized people well (you probably won't have that issue - but others might need to know that) and also, they will absolutely NOT let you take a bag onto the ride with you. They have these shelves at the loading of the rides where they will make you place your bag. The first time I went there, I was a little taken back by this. They do have lockers at the front of the park. When you go in, go forward a bit and the locker area is to your right.
The water park is WONDERFUL. And all the soda you can drink plus all the sunscreen you can use is FREE.
Bring a jacket to the cave even if it is 90 degrees outside. The cave stays at one constant temp all year - I think it is something like 57 if I remember correctly. The tours in the cave all vary. We enjoy them all - please know there is alot of stair climbing in many of them.
There really aren't alot of what I would call great restaurants near either of these places. We usally do alot of fast food on these trips. Someone who lives close may know of some local joint that I don't know of though.
If you are staying in Bowling Green, you might remember that the only Corvette Plant (and museum) in the world is there!
Bowling Green is about an hour from Nashville which has lots of great food and fun stuff to do - might want to consider that as well.
There are many "kitschy" little shops on the little 2-land road up to the Cave park. We love this one:
http://www.bigmikesrockshop.com/about_us.html
It is a hole in the wall place, but the kids love it and there are lots of crazy things they sell, plus they only charged us 50 cents each to go through their "mystery house." It has a couple of rooms with upsidedown water and such. Great fun!
One more word - BOTH of these places will eventually take you to little 2-lane roads to get there. Take heart- just when you think you aren't going to get there- you arrive!
Oh I forgot to say that parking is free at both places too!
Angie