Hi there,
Wisconsin Dells city is the place for you. It is considered the Water park capital of the world and which good reason. You can find both indoor and outdoor water parks here.
A great choice water park would be the Lost Rios
Waterpark at Chula Vista Resort. It is both an indoor and outdoor water park which features a wavepool, lazy rivers, and over twenty water slides.
The Kalahari Resort Waterparks is another good example. it is the largest indoor water park in the state and it features a stand up surfing pool, an uphill water rollercoaster and also an outdoor water park.
Accommodation-wise, it is best to consider one of the
Wisconsin Dells hotels or resorts that are actually attached to one of the many water parks.
The Atlantis Waterpark Hotel & Suites offers two Indoor Water parks for children 11 & under, 2-Room Family Suites with Whirlpools/Fireplaces, Poolside Bar and Grill, etc.
Hope this helps
VacationBuddy