Three suggestions after having made dozens of long road trips with kids. Get an early start, avoid traffic, and bite off as many miles on the first leg of the trip as you can. If your profile is accurate, and you're starting in Oconto Falls, I'd be rolling at 5:30 AM. That would put you past Chicago mid morning, missing the commuter traffic, and around Indianapolis by 2:00 PM depending on how often your crew needs to stop. You should be able to hit Knoxville around dinner time.
There are all kind of attractions and stuff to do around Knoxville. Calhoun's is an excellent BBQ place, some of the best ribs I've ever tasted. The Blue Ridge Mountains are striking this time of year, which you'd be able to check out on your next leg of trip (get off the Interstate). I 2nd all the previously posted recommendations, however I would hit them on the way back home.