MOMA in New York City. We took our kids and rented the children's audio guide. They loved it so much they insisted on returning there the next day. The audio guide was engaging and entertaining.
I enjoyed visiting the Evergreen Aviation and Space Museum in McMinnville, Oregon. Cool airplanes like the SR-71 and B-17 up close, with the Spruce Goose to top it off. Went midweek, so no crowds. My kids didn't seem to care much except for the 3D IMAX movie "Legends of Flight".