As you might expect, Boston has one of the nicest aquariums on the East Coast. If you are visiting the city with your family, the New England Aquarium is a great place to take your kids. There's the aquarium, an Imax theater, and whale watching (weather permitting), so you could easily spend almost a whole day there.
When I visit with my family (we are members, so we can get in free at any time), we start out at the penguin exhibit, which is my daughter's favorite. We have to pull her away, because while my son likes the penguins, he's always ready to move on first.
The giant ocean tank, which takes up four floors and is located in the center of the aquarium, is a huge draw. My kids can just sit forever in the windows, watching for Myrtle the giant sea turtle (who is older than me!) and the sand tiger sharks, along with the "regular" fish. There are also smaller exhibits on all four floors, including some hands-on sections.
The attached Imax theater generally shows nature-themed shows, although in the evenings, they sometimes show more adult-type blockbuster movies. Combination tickets, which offer a discount, can be purchased.
You can access the aquarium via the MBTA's Blue line, and there are also several parking garages nearby. Parking can be quite expensive, so public transportation is your best option if possible. Nearby hotels include the Boston Harbor Hotel and the Intercontinental Boston.
-- Jodi Grundig of Family-Friendly Boston and Multitasking Mommy
[Photo Credit: Flickr/pobrecito33]