[Noah930]

Kid-friendly stuff:

Museum of Science--great for kids.
The touristy stuff by Faneuil Hall/Haymarket. There are always street performers and big crowds on the weekends. I'd recommend the chocolate chip cookies at the Boston Chipyard and a slice of pizza at this hole-in-the-wall place called Haymarket Pizza.
The Commons/Public Gardens/the Duck Pond (did you ever read the children's book Make Way for Ducklings?).
A Duck Tour.
There's a water taxi that runs from around the Aquarium over to the airport and back.
Riding the T (subway).
Tour of the USS Constitution.
MFA (Museum of Fine Arts) over by the Fen. And if you're over there, there's the Isabella Stewart Gardner Museum close by, too. Maybe not as great for kids, but it's beautiful; it's incredible to think that (wealthy) people lived in places like this, and there's an interesting story of art theft from the museum, too.
Sox game. I'm not a baseball fan, but it's always a treat to watch a game at Fenway.

I'll actually be arriving in Boston the same date, but heading down to the Cape. Boston is one of the great American cities for a summertime visit, IMO.