To give some context: I'm not sure about exactly where in England they used to live, but the specific area they moved to is somewhere in either New Hampshire, Maine, Massachusetts or Vermont. The story's set in 2022.
Although I don't know if it makes any sort of difference to know this, the only other member of their family is their single father (their mother died a year prior), and they have no major financial crises to deal with.
Now, to actually get to the point: Would the children's accents change in any significant way because of the move (and, consequently, their placement in an American school), or are one or both of them too old to be affected?
ETA: Alright, so they'd need to be 10-11 or older in order to keep their original accents. Got it. Thanks for the help! ^_^