I love the Northeast in summer!
I'm near Boston, and there is a lot of variety. - When DS was a kid, we used to do the science museum, the various art museums, the maparium, the history stuff (of course!) and the library is awesome if your DD wants some down time.
South a bit is Plymouth and Cape Cod, North you could do Salem and Hammond Castle.
If you include NY state, we loved:
Howe Caverns, Lake George, and the
Finger Lakes (especially Watkins Glen State Park).
Southern Maine has some great little beach towns, and I agree about the puffin cruise. There's an animal refuge where you can see moose too.