A 15-year-old boy was sentenced to life in prison for fatally stabbing a stranger, Muhammad Hassam Ali, after a brief conversation in Birmingham city center. The second boy, who stood by, was sentenced to five years in secure accommodation. Ali’s family expressed their grief, describing him as a budding engineer whose life was tragically cut short.
Consider the alternative, or, rather, that really seems to be what you’re implying: That children are responsible for their own upbringing.
His upbringing isn't relevant to the issue. His deliberate actions are. He is generally responsible for his deliberate actions, regardless of how shitty a hand he was dealt.
We can give him some leniency on issues like contract law: He might not have the cognitive ability to understand an important legal document. He might not understand the value of money. He might not have the capacity for complex abstract thought, and should be protected from those who would exploit that and defraud him.
But Murder isn't an abstract concept. It's pretty simple. He isn't owed any societal protections for deciding to kill someone.