With kids... Mystic Aquarium (the seaport may be boring for kids), New London Sub Museum, Boston Science Museum, Plymouth Harbor/Mayflower II, Boston Aquarium, Faneuil Hall, If you want beaches and such then Cape Cod, Mount Washington (either drive up or take the Cog railway), Kittery, Freeport, Mt Desert Island, Old Orchard Beach, Nubble Light, Cape Elizabeth Light, Gloucester MA. You can keep going all the way to Nova Scotia and points north if you are so inclined. The drive gets boring at times since the ferry shutdown.
You can do a whale watch many places from CT to ME, many leave from Cape Cod.
Depending on your route, Fort Ticonderoga NY, Letchworth State Park. There is a 6 Flags outside Springfield Ma down river from the Basketball Hall of Fame.
Route 1 from Rockland ME to Mt Desert Island is pretty cool, but usually a very slow drive.
And of course there is NYC. which is certainly worth a stop.