Take a look at the recommendations on this page, plus visit http://vacation.away.com/massachusetts/travel-m2-cid2107-boston-cid350262-family-midattractionlist-p1-attractions.html. For something a little more fast-paced, take a look at these eight city-centric ideas from Outside magazine: http://outside.away.com/outside/destinations/200411/best_urban_adventures_13.html.