How do I require parental code on xbox 360 for adding new gamer profiles?

My kids' friends are adding their Xbox 360 Live and profile accounts to our system. How do we stop that using the parental code?How do I require parental code on xbox 360 for adding new gamer profiles?Honestly, I don't think you can. You can block the creation of new profiles but I don't believe you can block the recovery of profiles (which is what the kids' friends are doing).