Rehabilitation is ALWAYS possible in children and juveniles. Not guaranteed but always possible.
I don't want a system like in the USA where 13 year olds can be given life without possibility of parole because they're too young to be given the death penalty. Otherwise the state would execute them quite happily. Writing off an entire life in almost exclusively damaged and abused children and adolescents.
Many don't talk about what they've suffered until much, much later and their families don't either because it would usually mean criminal convictions for them. So you seem to have a dangerous child or adolescent who didn't have the best start in life but certainly wasn't considered to have it that bad. Till many months or years later when you hear about the rapes by family members or the paedophiles who bought them booze and games and were their 'mates'. Wandering the streets all day and often all night. Hearing Mum being raped and/or beaten by her latest boyfriend or punter or even forced to watch.Trying to climb out of the window at primary school age because there's no food in the house and no electric and parents are in a drug induced stupor or just fucked off for the night. Watching Dad kill your much loved pet because you've wet the bed again because you're terrified all the time.
Terrified of going to school because Mum cut herself again last night and says she'll hang herself today. Not being allowed to go to school because Dad has locked you all in a room because he thinks someone is going to come and kill you because he's psychotic.
That's the memories they have. There's also pre-language trauma that you couldn't express and can't consciously remember. Being left in a cot with a few bottles and a dirty nappy for days on end. Being in the house with your dead Mothers body for a couple of days before the Police break the door down.
These are the kind of backgrounds a lot of these 'evil' children and young people have.
I've seen children and young adults do abhorrent things (which are very, very rarely publicised btw) and go on to commit no other offences. Some do. It's not always easy to predict who will and who won't.
I don't excuse what they've done but I certainly sympathise and understand how it has happened.