idle hands are the devils workshop..
as for capitol punishment for children, strangely enough I think its more of a question of "can they be righted?", rather than the child's age.. though I suspect age would certainly be a factor.
in light of this trio's motive and their age, I believe these guys are among the worst humanity has to offer and IMO aren't worth saving.
I suppose it seems harsh but also IMO the kid they murdered was very likely a benefit to society and easily worth three of them.