What about camping? Or Door County? Or driving to a local "festival" - like the IL or WI state fair?
If you are considering local camping, we were very happy with Happy Acres Campground just over the WI boarder. It's very family friendly. Has a pool, a local lake, animals to visit, and events that are all appropriate for kids. They do rent out cabins too if you lack camping gear.
Door county has tons of rentals. There is a local petting zoo just outside of town. And the Penninsula State Park has an awsome beach, complete with a sandbar close to shore and rentals for boats. The town is very nice. It's very scenic to drive around. Depending when you go I think you can pick strawberries or blueberries also - the kids tend to eat more than they pick.
As for the state fairs, we haven't been, but we have been to several county fairs. The kids LOVED seeing all the animals and rides. We rented a lakeside cabin in WI, then went to the county fair one day. It was a lot of fun. And then we went "home" to cool off in the lake. The kids love fishing, canoeing, water skiing, etc. Even if they were too small, it was fun to go on the boat ride.
I hope the suggestions help. I'd find a fair, festival or attraction you want to see, then work backwards from there on accommodations. BTW - you can usually "hold" a hotel room without having to put down a deposit. The rates usually increase as the event nears and rooms are booked.
Sara