I am sorry you are going through this, and that he is as well.
How old is he? I was hospitalized at 17 and it was very traumatic for me being away from my parents, I can only imagine how a child would feel.
It's good that you are being proactive though, my SI tendencies started at 6 when I would hit my head and scratch, Sui gesters at 10. My mother ignored them till I was 14 when a school guidance councilor contacted her.
I am sure his pdoc will have some suggestions. I would ask if his meds could be causing Sui thoughts.... Mine got much worse when I started my meds at first...
Good luck, I hope he has some solutions for your family