"But I don't know anything about junior coaching" - surely that says it all.. he shouldnt be going on at the manager.. pretty sure his kid only started this season and there's already been two posts moaning about the team, the manager etcYou should talk to the manager in that case. In terms of what you say to your son, just be honest with him - tell him you’ll ask the manager.
Training. Should definitely be more than just games, there should be a structure to each session based upon what the team and each individual needs are, and then understanding applied in a game at the end.
Self organising10-year-olds should be given breakfast and then ushered out of the door with a jam sandwich and instructions to return for their tea. No need for clubs and teams - they will naturally self-organise all-day games of football.
Did you try West Didsbury and Chorlton?