I had the same problem. After talking with a tech support rep. I had to log into my sons account on xbox.com. it immediately prompted my child to have an adult log into there account. there was a link at the bottom that took me back to the log in page. i had to log into my account then it asked me to verify that i am an adult by entering my credit card information. It also said it had to charge my account .50 to verify that i am an adult. It says that all proceeds will be donated to charity. This is very frustrating that xbox would have to charge my account to verify that I am an adult. If all xbox customers have to do this that is roughly 23 million dollars. Seems like a scam to me. Might be time to look at Playstation.
Hope this helps.