Hi chrissa275!
I understand that your son is unable to access his Apple ID account, and I'm happy to help. It sounds like two-factor authentication was enabled on his account, and you can find more information below:
What if I don’t have access to a trusted device or didn't receive a verification code?
If you're signing in and don’t have a trusted device handy that can display verification codes, you can have a code sent to your trusted phone number via text message or an automated phone call instead. Click Didn't Get a Code on the sign in screen and choose to send a code to your trusted phone number. You can also get a code directly from Settings on a trusted device. Learn how to get a verification code.
If I can't sign in, how do I regain access to my account?
If you can’t sign in, reset your password, or receive verification codes, you can request account recovery to regain access to your account. Account recovery is an automatic process designed to get you back in to your account as quickly as possible while denying access to anyone who might be pretending to be you. It might take a few days—or longer—depending on what specific account information you can provide to verify your identity.
Two-factor authentication for Apple ID
Cheers!
