A minor is a legal fiction it can and will be discarded when convenient. Many people either don't understand or pretend not to understand that order is the only thing preventing so called children from killing and eating you.
Criminal gangs specifically recruit legal minors because they are able to do things legal adults can't: Repeatedly and with impunity violate the law. Whether it's smuggling or assassinations, using legal minors make it all a lot less risky.
Would it stop stupid kids from doing stupid kid stuff? No. Would it make minors less attractive to organized crime? Yes.
No. For both children and adults, sentencing strictness only deters a SINGLE category of crime--white collar.
Most other forms of crime, especially violent, are almost completely insensitive to the harshness of any possible punishment sentence.
If a brain is sufficiently broken that it no longer has the limiter against harming another human being, prison sentences won't do anything to fix that.
Wikipedia article makes no obvious mention of correlation between sentencing and deterrence. Linked article, in fact, demonstrates that alternative programs provided almost all the improvement.
Many people understand that criminal law is like a bandaid. You apply it after the bad thing happened. Sure, it may be a common believe that the punishment formulated within it also scares away new or repeated criminals, but that is way worse at getting the job done than common sense measures that prevent people to slip into crimes to begin with.
I can't remember seeing countries with stronger protections for minors collapsing into a perfect spherical body of criminal children. Good juvenile justice systems are not about the absence of consequences, they usually are about age-appropriate consequences instead. In short: supervision, intervention, and rehabilitation instead of pretending a child is simply a small adult. The idea that only the threat of adult punishment prevents children from “killing and eating you” is so simplistic it is an insult to everybody forced to read it.
If a kid becomes violent usually you have a long history of publicly visible and known smaller, less dramatic events leading up to that. Good social work and educational systems are able to pull children and teenagers out of that spiral, by for example isolating them from destructive family dynamics. All tried and tested, papers written about it, statistics and studies published about the effectiveness.
Countries having problems with criminal minors are usually countries who try to not spend any money on social measures and education. Or put guns into the hands of kids. There aren't many such countries.