Family RV road trip- Mount Rushmore/Yellowstone/Grand Teton

Instead of stopping in Madison Wisconsin, go to the Dells and spend a day at one of the water parks. We're doing this en route to the badlands this summer and we're also from Michigan. Your kids are perfect ages for that.

You could come home through the UP and stop at Voyageurs national park. If you like to kayak that would be interesting. Maybe en route to Voyageurs, stop at Theodore Roosevelt national park in North Dakota. But that's if you're a national park junkie like me. ;-)
Have a great trip.