This was probably one of the hardest days for us when we finally told our son (he was 6 at the time) that he had BMD.  We waited to make sure of the diagnosis - which for us was via a genetic test.  Like Roxanne, we tried to keep the conversation simple.  Basically we started the conversation by ackowledging to him the fact that he'd been to the doctor for several uncomfortable tests.  And told him the results of the tests.  We shared, like Roxanne, that this one was reason that he had some discomfort in his legs when he ran alot or that he didn't like to race his friends.  For our family it was difficult for us parents - but there was a look of relief on our son's face.  Finally he received a name and acknowledgement for what he had already been feeling all his life.  For us, it was a time of grieving and for him a time of enlightenment.  We went through a few years as parents trying to come to terms with what this means for him (and his little brother).  He has asked questions along the way at random times.  Like last year in the middle of Dick's Sporting goods he blurts out - will I have to use a wheelchair someday?  And at his PT appt just two weeks ago he was very angry at the notion that everyone can play on a trampeline but him....  (He's 10 now).  I think every family has to determine what works best for them, but we try to focus on complete honesty and simply try to answer questions in a way he can understand.