It’s possible and I understand the fear there. My daughter six weeks ago was beating her head against the wall regularly and throwing things. In the past, she’s attacked my son, a classmate, and our pets. I would suggest just responding to the situation if it occurs and try not to borrow trouble that hasn’t arrived yet. Be aware and alert for it, but realize that might not be the outcome for your child. Most people with SCZ are not violent. Even so, there’s nothing you can necessarily do until it happens. There’s not a way to actually prevent it, as far as I know, other than taking some basic precautions (locking up knives, meds, guns, poisons, possible weapons). Realize that a nonviolent restraining may be necessary (for my daughter I get behind her, wrap my legs over her legs above the knee, hold her arms, and just keep my face out of the way of her thrashing head, or I do a bear hug from the front. She will beat her head against my shoulder but usually works to calm her down). I realize with a boy this may be harder so you may want to talk with your therapist or psychiatrist about the best methods.
I agree with @hope there are some threads about younger kids (I’m one of the posters) so if you search for child or early onset you might find some good results within the forum.
Here’s one example: https://family.schizophrenia.com/t/early-onset-childhood-schizophrenia/4759