This can leave a bad taste in the mouth. For example, I would try the two girls in the "Slender Man" stabbing as adults. The main point in juvenile justice should be severity of offense, and I base this on the utilitarian concept. I wouldn't feel like a hero of the Republic for that decision, but I think it's the right one Perhaps a better overall fix would be to assign the juvenile courts the ability to issue severe penalties while still separating the juveniles from the adults; "separate but equally harsh"
The other side of this is when the State fails to assert parens patraie in cases of negelected or abused children. I won't even look up cases in which the State has lost children, or worse.
In either case, it comes back to the point where we leave theory and enter the world of resources and politics.
So there is a valid "right versus right" argument. Mercy for monsters with the appearance of children versus justice, and the future protection of society. That sounds biased against mercy, but I'm not sure I can balance the statement out from my perceptive.
I wonder if tribalism plays a part in this thought process; I'm not big on race or social status as far as I regard people that are "on my team", but people that kill, rape, or steal, regardless of mens rea, are instinctive "others". I'm not worried about their intent, background, or motivations...I just want them AWAY from me. I think this is where retribution as a factor in criminal justice comes from for many people.
I do know that confining children with adults is disproportional, considering our society's reluctance to make prison a safe place for prisoners. I don't think it should be a "painless" place, as "pain" is a function of punishment. But that "pain" needs to be a measured instrument of the State, not simply more crime committed by other prisoners.