Let's make one thing really, really clear here. You owe the coach and the organization nothing. Period.
Anything a parent says as to why they are moving on can and may be used against them in the future. Coaches and G.M.'s move to different organizations and word does get around. You would hate for anything you say to be held against a 13-14 year old kid.
Shut your mouth and move on.
Again, coaches talk to each other especially at the older levels. Unless your just bouncing around from 1 low level team to another your best option would be to tell the coach or someone in the organization that you plan to leave.
I agree, and as someone who coached in the past, the caveat here is many of the coaches do talk - however, the good coaches who love the game and helping kids continue to do so usually take what other coaches say with a grain of salt and are aware that there are two sides to every story.
I always did, and found that most of the time, even kids/families that were spoken ill of by others usually are fine with a new organization that spells out the expectations and philosophy from the very beginning.