The Minnesota History Center, which includes both a museum and a library, has several different history exhibits, including one that rotates on a regular basis. I spent about two hours browsing through the exhibits and thoroughly enjoyed my visit.
I lived in the Minneapolis/St. Paul area for five years as a grad student and never made a visit to this history museum. Boy did I miss out! I hope an opportunity presents itself to take my daughters to this museum as I think they would enjoy it.
If you ever find yourself in the area, take time to visit this museum for a morning or afternoon. St. Paul also has a great downtown area with other things to do (they have a fantastic science museum) as well as many amazing places to eat!