I took my three kids and a niece, who are in grades 1 to 5, to the Museum of Mathematics on Sunday, and they liked it, spending almost 2 hours there. The exhibits are "hands-on", and they could bicycle and run around (in the exhibit that uses lighting to divide the floor so that each child stands on a different color). There was a musical exhibit, one demonstrating fractals, and many illustrations of geometry and topology. A gallery of exhibits is at http://momath.org/gallery/ .