As the whole story has not been reported, and this child may turn out to be a bully preying on children smaller than himself, you still do not handcuff an 8 year old!
As much as I hate to, I must disagree. If I were a LEO, I would definately handcuff ANYONE I was transporting. An 8 year old kid will kill you faster than an adult. And I am sure the kid already knows how to use a gun and knife. This kid, who obviously doesn't have any respect for law and order much less other people, has already shown his ability for violence. HAndcuffing is definately merited, and probably dept. policy.