There's also some travel possible to Montreal, via train, though it's a long ride. 8 hours, doubling the time it would take to drive there. Same with Boston, incidentally - train rides nearly double the length of your trip. Not sure it isn't just worth waiting till the babies can handle the car. Sigh.
I have been wanting to be a bit more proactive on US history - and Boston and New York seem to both be great ways of exploring origins. Zar's identified Chinatown as a must, though she's really interested in the knock-off shoes. My mom wants to see the Intrepid, though I'm not sure I can handle having my mom on an overnight trip.