According to the Fallout wiki the Children of Atom spread from DC to the Commonwealth.
However, you'd think if there were ever going to be radiation/nuke/atom worshippers around the Commonwealth they would already have set up in the Crater of Atom, given that it emits big streaks of green irradiated dust high into the air and can be seen from the other side of the Commonwealth.
Anyway, if the Crater of Atom is the result of the nuke fired at Boston, and it created the Glowing Sea, still heavily irradiated 200 years later, yet Boston largely survived despite being relatively close, then what do you think New York City is like, given that it was directly hit?