A Microsoft file hosting and synchronization service.
Hello,
Do you see your son's email address on the Verify Your Identity Screen?
So, you can no longer receive a Verification code at that address to sign in to your Microsoft Account?
If yes, and you do not have any other Security Verification methods to prove your identity, you will have to replace them.
That is, on the Verify Your Identity Screen, select 'I don't have any of these' and follow the prompts to replace the Security information.
(Ensure you're on the same screen as shown in the screenshot above.)
Note -
If you remove all of your previous security information and replace it with something new, your account will be put into a restricted state for 30 days.