Kalahari: Just visited this week for the first time. This place is awesome. My kids are both 6 and they had a blast. At this age they can do just about everything there. Best indoor water park in Ohio. Great way to beat the winter blues!
Pewits Nest. Just a short drive away from the waterparks of Wisconsin Dells is Baraboo, Wisconsin which has some pretty amazing natural areas. Whereas Devils Lake State Park is the big attraction, Pewits Nest State Natural area is a local gem.