Kayla,
First off, welcome back and congratulations! M2 gave a very good summary of EFMP a while back (though that last link is now dead), but here's some add-on.
Definitely. You can be put on EFMP status for something as minor as a child with ADHD. In the end, it is the AF trying to make sure that you will have adequate care for your family, but you'll find that the paperwork and hold ups can be a MASSIVE pain in the ass, so do everything you can to lead-turn this and be proactive (i.e. don't trust the EFMP office to have a sense of urgency).
Not necessarily - it all depends on the facilities that are available where you're going. Part of the reason EFMP is a pain in the ass is that the medical facility (specifically, the EFMP coordinator) where you are currently stationed needs to coordinate with the medical facility where you are going and ensure that they have the right type of clinics, therapists, facilities, etc., that your son needs. We just came from Germany, where - in addition to a full base clinic at Ramstein, they have Landstuhl Regional Medical Center - the largest US medical facility in Europe. I do know that England (Lakenheath) has a full-up hospital on base (as opposed to the clinics most bases have), so that isn't necessarily out of the question either.
I would suggest you call the EFMP office at Pease and see if they can determine the possibility going to either of those three locations.