I have the answer to our problem DMX Aceman - it's been sorted for me so I hope that I can help you.
I phoned Xbox support (for me it was an 0800 number as I am from the UK) and I was told to do another password reset form and email it there and then (for the parent account). I came back to me and said that I haven't supplied enough information so the guy on the end of the phone told me to read him out a little number at the bottom of the screen. After about 35 minutes, I had the email address that I had used when I set up the parent account and thus only needed to reset the password.
A couple of hours later, I received an email from Microsoft Xbox Customer Care Advocacy Team about my issues with resetting the password to the parent account - if you give enough of the information to Xbox support over the phone they send your request to these guys.
I didn't reply the same day so I received another email asking me again but making me politely aware that if they didn't receive a reply from me in the next two days that I would have my request closed. The email asks you to fill in lots of details, as to make sure it is the account holder they are conversing with. I sent the information email around 7pm at a few hours later I received the password reset email and have now got an adults account.
Moral of the story: phone Xbox support - I truly recommend it.
I've been having problems since the update in September '12 and it got sorted in 3 days.
Hope that this can help you? :) x