We visited the Mpls Sculpture Garden with our two young-ish sons after a busy day of driving.
This attraction is free (parking is not, but at $3, it's a bargain) and has a fantastic collection of oversized sculpture, all of different origin and purpose. It is really a large park at which kids (and adults) can stretch their legs and have a cultural experience at the same time. It was extremely hot (93F) when we were there, and we were grateful for the varied exposures of the pieces; some in full exposure, some shaded by beautiful trees, gazebos, etc. There is also a killer view of the Mpls skyline from most places in the garden.
Highly recommend for anyone, whether alone or with family/friends!