What kind of things are you looking for? How old are your kids? The museum of science is a lot of fun, we're members there because we go so often. The Children's Museum is a lot of fun up to about age 10 or 11 I'd say. It's more like a science investigation place than a traditional museum nowadays, lots to see and do. The Aquarium isn't bad but it's quite pricey for what it is, we rarely spend more than 2-3 hours there and half of that time is spent looking at the penguins.
If you have history buffs in the family a walk down the Freedom Trail is always good. Quincy Market is good for lunch because there are a few dozen different options all under one roof. Best to go a bit early or late though, it gets really crazy around noon. A ride on the duck boats goes over well with kids too and you'll see a lot of the town that way.
at 1:48 PM on Aug. 31, 2009