We live a couple hours away too, and visit a few times too.
Blue Man Group was pretty fun! (don't sit in the front though unless you want to get wet) Never done Medieval Times, though.
Don't forget about Brookfield Zoo! Or even Lincoln Park zoo, for that matter!
Check the calendar for your dates so you can see what is going on...
Maybe you can take in a sporting event?
Lists & Calendars of Chicago Events - Activities from Chicago Traveler