I had ALL at eleven and I didn't want to take chemo either. I wanted to go home and pretend there was nothing wrong with me. My parents didn't listen and I went through five years of chemo. Thinking back, I'm so glad I did. It was hell, but I'm relatively healthy now and I have two beautiful children.
I can understand if there were no hope of a cure or remission for this young man. Then I would say why make him go through with it? Let him enjoy what time he has left, but he has a 95% chance of being cured.
When he's thirty I can't see him asking his parents "why did you make me go through with it?" I see him saying "thank you for getting me the treatment that I needed."
JMO
If there's a way to send this boy your message, you should do so. It's very inspiring and may help him. Please consider doing it.