My son has forgoten his apple ID password and sign in is locked because he has tried too many time

See if anything here helps.  If necessary, you can use account recovery as explained in the link at bottom of the article.

Verification code - how to get one and sign in with two-factor authentication.   

If you are locked out of your Apple ID account you can go to https://iforgot.apple.com

This will provide you with the recovery steps you put in place for this situation.

Here are some support articles that should help:

If you forgot your Apple ID password - Apple Support

If you forgot the answers to your Apple ID security questions - Apple Support

If your Apple ID has been locked or disabled – Apple Support