I have done years of research in the field of youth sports. Probably as much as some researchers have. I have also coached football for many years with great success. What I mean by success is that I have winning teams with happy parents for what I accomplished with their kids and every kid gets to play the entire game.
The local youth rec. football league in our town has a minimum playing
time rule that each kid will play the whole game on either offense or
defense. It's a good rule and it works. I have yet to hear one kid or
parent ever complain about this rule.