First team?under 21 training

Does anyone know how to stop your under 21 players training with the first team with an english club, keep getting players unhappy with training as theres 40/50 players being trained at the same time, sometimes move players to the under 18 squad but there must be an easier way than that?

Why are the players unhappy? I don't think it will be because of the amount of players being trained (unless your coaches have heavy workloads and in that case get more coaches)

My players always bitch and moan about training because I have them learning new positions, its a balancing act. I wouldn't for example ask a player to learn a new position, learn a new trait, work on a specific attribute and do normal training on top of it. You don't want to stretch them too far.

Some players will just bitch and moan for the sake of it, just like in real life. If its becoming a serious problem then look to get more coaches or rework your training schedules.