A lot depends on which route you are taking, and if you are going to Boston (Eastern MA) or Western Mass. There are all sorts of great kids-related stops in PA if you are willing to take a more westerly route: Hershey, the Crayola Factory, Sesame Place, etc. If you are staying more easterly, the Mystic Aquarium in Mystic, Connecticut is great and Newport, RI has an amazing colonial port and some really great old houses to see.