This won't be a camp issue. Bullies will continue to do similar things after camp, if it is allowed. Leaving school will stop the issue for the nephew, but not others. Leaving the team might not stop it for the nephew. Not reporting this is such a bad option. At a minimum the principal needs to be notified. Likely the nephew is in for ongoing issues, regardless, if no one does anything:
https://www.cougarboard.com/board/message.html?id=33272128