No. What is your goal? Development or winning games? You have a great coach and team, you are done. So what if the team has 12 players. The coach is great, development is presumably good. The players will get lots of playing time, won't be much standing around at practice and while a few games might be lost due to lack of subs, who really cares?
Also, be mindful of the fact that players from the same club can be "passed" to various teams throughout the season. My kid was on a "B" team with 9 players by the third game (injuries), a few kids from the "A" team were loaned and so were a few kids from the younger "A" team. It worked fine. Its one thing if you don't have enough players in the club to field a team, but finding a good coach and teammates is the quest, winning is just a byproduct.