Something fun to do with the little one in Boston.
The Boston Science Museum makes for a lovely day out with the family, especially at the moment when they have the Harry Potter exhibit.
At the moment it is $26 a ticket for the museum and the Harry Potter exhibit, but one thing to consider, get a library pass card from your local library as it'll save $30 on admission for a pair of adults, the pass allows up to 4 people. Kids under 3 go for free which is really nice.
Definitely bring a push chair for the little ones as the place is pretty huge and will take much of the day to get around, but well worth it. Parking at the museum is in a multi story, and is around $16 for the day which is really good.
The cafeteria isn't to badly priced and the food generally isn't all that bad, some of it better than usual and some typically cafeteria fare, but over all not bad, especially for the kids.
There are plenty of bathrooms and water fountains through out the place as well as lifts making it easy getting about and taking care of little ones.
Plenty of extra shows that cost extra, but the butterfly exhibit is a good one and worth the money, certainly for little kids, the others probably not so much, certainly for little ones at least.