I'm interested in why you think this way. It's controversial, but don't think there is conclusive evidence to that. With no proof of true randomness in brain processes, and Libet and Haynes' experiments showing you can change your mind after your brain received signals, we can't say it's fully either random or determined. Humans are poor at randomness, too. The brain is also unique, in the sense no other mechanism can learn from the exterior and create their own instructions, all by itself. Yes, it can be influenced, but saying all free will is false is a bit extreme, imo.
There have been attempts at manipulating choice with stimulation techniques, and, while the desire can change, none could achieve a 100% rate. The last word is up to the person, and every experiment seems to reinforce that idea. All we know about the brain is compatible with event-caused free will. Even then, many types of compatibilism are still an option.
The child brain is literally undeveloped. There is a reason so many mental illnesses develop during childhood or teen years. Sure, adults can have trauma too, but they are more prepared, and it won't last all your life, as it's the case on youth.
