The MIT Museum is small (about 1 hour to see everything), but fascinating. This museum has the world's largest collection of holograms, and many are on permanent display. Other exhibits include Rube Goldberg type contraptions and amazing stop-action photography (by the pioneer of that approach.) There is an area for children to play and color, though many of the exhibits are too exposed for small children. (You'll be running after them the whole time.)
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