Handcuffing is not assault, only in the minds of the general public. It is meant to restrain someone, from doing damage to others or themselves.
So they had to handcuff a 5 yr old who was having a fit, and a history of this sort of thing... in my mind that is not assault. Yet people read "5 year old" and automaticaly gasp.
When your child is having a temper tantrum and you send him/her up to their room and punish them not to leave for a few hrs, is that not restraint of a certain level? Perhaps not as extreme, but it is in the same grey area.
the best of you