I second Lisa's idea of going to Minneapolis. Not only is the Mall of America great for adults to buy clothes WITHOUT SALES TAX, but there are a ton of other great places in the Twin Cities.
The MOA has an indoor amusement park, Underwater World, mini golf, a movie theatre, Lego Land, and lot of other good attractions.
In St. Paul there is a fantastic Science Museum and Children's Museum. There are also fantastic parks all around, including Como Park which has walking and bike trails, a FREE zoo, kid-friendly amusement park rides, lake with paddle boats for rent, conservatory and a lot of other things.
Minneapolis has the Walker Art Center which I vividly recall visiting when I was a child. You could also take dinner cruise on the Mississippi River, of rent a boat and go out on any of the 13,000 lakes in the state. TONS of stuff to keep you busy in the Twin Cities!
There's also a great semi-pro baseball teama called the St. Paul Saints which is supposed to be a very family-friendly atmosphere and has a whole lot more going on at the stadium than your typical MLB game.
If you visit near the end of summer, right before Labor Day, you could even go to the MN State Fair which is the 2nd biggest in the nation (right after Texas).
Have I sold you on MN yet??