Hi Papa,
this is an interesting dilemma you face.
I'm an under 11 coach in the Australian system and i think our setup would be perfect for your son, however probably to the detriment of the game (unfortunately). Our junior program works on a rotation policy, so everyone gets an opportunity to bat and bowl during the course of a game. We play 25 overs a side and each child must bowl at least 2 overs each. With the batting side of things, every batsmen gets 12 legitimate balls each (not including wides, no balls, etc), then they have to retire and let the next batsmen come in. Once retired you can resume your batting if other batsmen get out and your team needs you at the end of the innings. Each week, every player must rotate positions to experience every role possible in a game.
Now this may sound ideal, as it gives every child the opportunity to participate in a game and improve in match situations, however in reality it frustrates the life out of me and i personally don't think it works. I think it breeds mediocrity as it rewards the week and punishes the strong, with the weak not expecting to earn their position in the team. Additionally, the best players miss out on opportunities to excel and can become frustrated and disillusioned with the sport because results don't pan out the way they should. It keeps the weaker playing in the sport longer, who probably don't have the passion to be a long term player. If you make life easier for the children and give it to them on a plate, they will not grow as individuals or athletes...... Survival of the fittest (natural selection), so to speak.
I think every child needs to earn his position in a team and by being exposed against and playing with better players, this will eventually make your child stronger and more competitive in the long run. I have purposely enrolled my child out of his age group and he is playing with children older than he is. He has adapted well and is very competitive with the older boys and more than holds his own, even though he is one of the skinniest kids in the team. In saying this, if he played in his own age group he would most likely be in the best 2, however i would prefer to challenge him as i think it will benefit him when he rises up through the ranks.
My advise, is to keep him where he is if he is enjoying himself and give him extra private training in between so he improves with the additional practice. Only move him to another club if he gets frustrated with the sport and wants to give it up. You will find if he has a competitive streak, he will naturally rise to the challenge when given an opportunity.... lets not also forget, with children of this age there can be massive differences in physique and size causing disparities in performances and this will differ as each year goes by....... the big fat lad usually dominates early on, then falls away when the skinny athletic lad gets stronger as he gets older.
Hope this helps.