Cave of the Mounds in Blue Mound, Wisconsin is a great stop for kids. It's just of Hwy 151, between Dubuque and Madison. The cave was very cool to see and I definitely recommend visiting. Tours are self-guided but they assign a time for you to enter the cave when you buy your tickets, in order to stagger the groups of people.
While we waited for our tour time, my son enjoyed the gem mining sluice and then using the posted guides to identify each gem. I really like the self-guided nature of the cave tours because there were plenty of guides available inside the cave for those who wanted more information, or you could move faster if you had antsy kids with you.
When buying tour tickets, they ask if you want to rent or buy a black light (it's $10 to buy a small black light or rent a large black light). We bought a small black light and my kiddo enjoyed using it in the cave, but it didn't really add a lot to the cave tour.