Stands to reason that if a child is being restrained and can not breathe that he will fight harder right before he dies.
Seems a responsible person would release his hold if the kid's struggle for life escalated or spiked beyond safety, at the very minimum, ask the kid if he can breathe. If the kid doesn't respond, chances are good he can't and the hold should be released.
Restraint induces high stress and is too risky to be used on kids, particularly by young, inexperienced, and/or sadistic staff.