My advice is to try not to get ahead of yourself worrying about every worst case scenario. If your son has concerns I would encourage him to talk to the leader and to make his needs known If he doesn't want to do that now I'd say it is fine if he wants to wait until a specific scenario comes up. I would never underestimate the power of a child being highly motivated to succeed at any activity creating the opportunity for them to overcome some challenges. That isn't to say he's going to be able to run marathons, but that he might ride out being cold or tired much better when he's in the moment with an activity he enjoys (than he would if he was at home with a worried mom). I understand the desire to protect him from hurt...but that can also prevent him from growth too.