Kristina,
Can you hear 'it's a small world' playing in the background right now? :) We are relatively new to Bardstown but we LOVE it here - this is a great little town, and a great place for families.
For your girls I would recommend Blizzard Beach. There is an entire kiddie section of the park called Tikes Peak that will be perfect for them. There are small-scale waterslides and raft rides, a zero-entry pool, and really cute fountains to play in. Check out
this page for more info.
A couple of other things to keep in mind at the water parks - you can get refillable mugs here, which can be a big savings if you plan to spend a lo of time there. For the most bang for your buck, get one mug and share. Also, towels are rented here for $1 each. They aren't the big beach towels you're probably used to, so you may want more than one per person. You can bring your own with you, but I think that's enough of a hassle that I'd rather pay the rental fee than fool with packing one more thing, or lugging the wet heavy towels back to the resort (and then home again).
Have a great vacation!