We spent well over three hours there with our 4, 6 and 8 year-old after planning to be there only two. Though afterward my oldest daughter thought it was mostly for younger children she enjoyed all the activities and we had to call her three times to get out of the massive climbing structure in the lobby! Lots of rooms with fun, semi-educational and very hands-on activities. Though the line to get in was long it didn't seem that busy inside. Expensive afternoon (almost $80 for our family of five) but my youngest two enjoyed it more than any other museum in Boston. I would definitely recommend it if anyone in your party is under 9 (the adults were having as much fun with the activities as their children!). Didn't see a lot of staff in individual rooms; they were congregated mostly in the entrance and at a couple of areas (art room, "kindergarten" room) and they didn't seem terribly engaging in dealing with the children. Most kids were just having their own fun with parents or other children. Lockers are available in two sizes for a quarter (which is returned upon emptying).