To confirm that you are an adult as defined by the FTC's children's privacy rules, you are asked to provide a valid credit card number. This step is required to verify your age only. Your credit card is not charged any amount. As soon as your credit card information is verified, Windows Live discards your credit card number. During the verification process, a temporary $1 hold is placed on your credit card account. The $1 hold is not a charge, and it is removed from your account according to your credit card issuer's policy.
Once a child becomes older than the age required by the United States Children's Online Privacy Protection Act (COPPA), that child will no longer be listed in your Manage your child's account area.