I see where you've spoken of having a brass band. I have a question for you if I may. My 11 year old started playing the alto sax this school year... he's shown great promise but not great commitment. He practices 1 or 2x a week (in addition to band practice at school) yet is as good as any of the other kids who may practice more. He has picked up really quickly at reading music.
Problem is, he says the sax is too 'hard' to play and wants to switch to trumpet. I think he is only saying this because the sax seems more complicated, is more cumbersome to hold and harder to take care of.
My question - do you think the trumpet is any easier to play/care for? I don't want him to get discouraged from band, and would let him switch if it keeps his interest, but if it's just as complicated I would encourage him to stay with sax. (As I said he shows remarkable natural skill).
Trumpet is just as difficult to play well as is alto sax. And alto sax is no more difficult to play well as is the tuba.
In short, at your son's age, he is probably influenced by a friend or two who play trumpet and he wants to join them. I agree with those who say to go along with him on that and rent a trumpet (or pick up a beginning level horn on Ebay) on the cheap.
Personal story - in 1968, in 7th grade, I began my musical odyssey by playing French horn. It was a single horn in F. I lived over a mile from school and would either walk or ride my bike. If you've never seen a French horn case, let me tell you that carrying that damned thing is a major league pain in the ass. It constantly bangs into your leg with every step due to the size of the bell. Even on a bike, it was awkward and even dangerous. I was actually going to quit band over it for the simple reason that I just didn't want to drag that damned thing home with me, but the teacher talked me into playing trombone instead. I played trombone throughout the rest of my public school daze and managed to teach myself how to play euphonium in the process, which I took much further.
Had I not been permitted to play a different instrument than I one I was "assigned" to begin with, I might've wound up working in the freakin' auto industry on the assembly line. That would've been an early death sentence.
I think the music education people will tell you that kids who learn to play an instrument -- any instrument -- or sing encounter enriched development of the right side of the brain beyond the norm. You could read up on that if you were so inclined. Right-brain development nurtures the creative side and the non-analytical methods of thinking.
Bottom line -- let him play trumpet.
Now, if your son has lips the size of doughnuts, he could have some physical problems with playing trumpet that may not become apparent initially. But if there's a will, there's a way. People find ways to work around problems if they're truly interested.
Your son may not make music a career, but he'll be enriched and likely better developed if he continues to play an instrument.
Good luck!