My parents took us to the Dells almost every summer.
I recommend the Wonder Spot. It's somewhat hokey, but it's definitely interesting and pretty low rent.
If you have a fist full of dollars, then by all means 'ride the ducks'! Not the cheapest ride in town, but definitely a fun way to kill a few hours with the kiddies.
Big chief coaster world has a good selection of coasters and go cart tracks. If you get REAL hungry, try Paul Bunyan's "Northwoods Cook Shanty". Served 'camp style', they bring the food to the table in big serving dishes so you control your own portions. The food is pretty good, and the kids will love the experience (I always did)
Main street has a few interesting museums and shops among the tourist oriented t-shirt shops and arcades.
There are still a few goofy golf establishments, although the best ones are gone. Most are just glorified putting ranges, not really 'goofy' at all.
The jet boat ride is worth the high price.
the Mid Continent Railway museum is a fun ride for kids and adults will enjoy it too.
If you still have any cash left, your kids might like Tommy Bartlett's Water Show and Robot Museum. It's a P.T. Barnum style, tourist trap legend.
Have fun!