The Original Wisconsin Ducks is one we love and repeat and I highly recommend it if you haven't been (is this your first time to the Dells then?).
Noah's Ark is that where you're going for a waterpark, if so you won't be disappointed.
Other than that what are your likes and interests (nature, museums, quirky and fun stuff, outdoor activities) as a family and I can definitely share more suggestions.
Are you interested in branching out and seeing some sights in the area other than the Dells or keep a solely Dells focus? Baraboo is a great choice, even The House on the Rock in Spring Green, if time allows.
For the pricepoint for hotel perhaps the Kalahari or Wilderness for its offering for the ages you mention. They both have different things to offer. Check the websites and reviews. Chula Vista is one that gets good reviews though I hear less of it. So that's another you might consider.
Edited: 12:05 am, March 06, 2012