I just got back from Boston 3 weeks ago. It is a fantastic place, as ladylex says, the Freedom Trail is excellent and buggy friendly except the last bit on the boat. Shopping is easy with a buggy in the Prudential Centre and Macys but probably not great round Newberry Street where all the shops are the road, not in a mall. Boston Common is lovely to walk around. If you have a sitter, there is a restaurant in Cambridge called Oleana which is fantastic, they might be child friendly but I didn't see any in kids in there.
http://www.bostonusa.com/
This is not a bad website. Have a lovely time, it's a great place.