Thank you all so much for your messages.
We have spoken to DS and told him that I had looked at his phone and seen a couple of things that worried me. Firstly the fact that he thinks so little of himself and then he clearly knew what the other was.
It turns out he has tried it 3 times over the last two weeks with the next door neighbour in a local park. Another friend also tried it once.
We approached it in the vein that we weren't going to punish this time but that we wanted to make sure it didn't happen again. We explained about the mental health effects, he said he didn't think it was even harmful as they use it as medicine in the states. We explained the rare circumstances of that and the cnsequences on the growing brain. I said I'd get him some information when he gets back from camp and wanted him to read it so that he understood. He agreed.
He seemed full of remorse and was genuinely ashamed of himself which is hard as he has such low self esteem. We said that we'd expected it to happen at some time but not for a few years he was bowing to peer pressure and not to blame himself. We approached it in that he had made a mistake, we'll draw a line under it and no consequences this time but if he ever does it again there will be strong consequences. We agreed not to tell the parents of the other two boys but we will do if it happens again and we know the NDNs well, the dad would go mad and he can be scary and DH has the other boy's mum's mobile no so he knows they are not idle threats.
We said his friends can come here any time, and actually we redecorated the playroom to be more of a teen room just at the weekend for that purpose. We also said that he is not allowed in the relevant park where they had been going and doing it.
All in all, the conversation went well. He is very remorseful and grateful for us not going mad and understands the consequences if it happens again.
We also talked about his low self esteem, did our best to reassure him that others aren't better than him and said we're always here for him. We also asked if he could think of someone else he could talk to as we understand parents aren't always a teen's first choice of confidante. We asked him to give it some thought.
All in all, I think it went well, we didn't alienate him and will keep a very close eye on him now.
Thank you all very much for your input.