The first thing is to test and make sure the filtering is really in place. On the network, try to go to http://filteraudit.cjclds.net/
and see what results you get.
Are you sure the youth got into YouTube via the church's wireless and not his own dataplan or a unsecured neighbor's wireless?
If it is though the church system, then I'd make a call to Global Services and advise them of the situation. I'm not sure if they have logs they can check to see if they can spot the proxy and report it. I believe by default known proxies are blocked. But if the youth set up his own proxy at home, it's probably not known to any of the filters.