Hello FRS019!
Thanks for touching base here in Apple Support Communities. I understand your son doesn't have a driver's license and thus cannot verify his identity to use Apple Pay Cash. Check out the information below for an explanation of what he can do:
If your identity is unable to be verified, you won't be able to use all the features of Apple Cash, including sending and receiving money and adding money to your Apple Cash balance.
You can use the money on your Apple Cash account to make purchases in stores, in apps, and on the web, and you can transfer money to your bank. "
Identity verification for Apple Card or Apple Cash
Please keep in mind that a state ID card can be used in place of a driver's license for verification.
Warm Regards.