It depends on the local circumstances and policies. I can't imagine they will refuse check-in if the son looks his age and has a convincing story. IF they refuse to check in the son because of this reason though, son needs to ask dad to fax a certification with cardholder signature and a copy of credit card. If the son is very young or is stressed, the agent may (or should) be willing to call the dad instead and explain the situation. The agent may opt for a verbatim verification if it would take too long to obtain a fax.

You could argue that faxing a CC compromises card security, but then again this was pretty common before the internet days. The agent should still confiscate the fax on the spot after completing verification though (I would insist on it).