To create a Family Account, you must certify that you are at least 18 years of age and the parent or legal guardian of the children you add to your Family Account.
While there are no foolproof ways to verify over the Internet that someone is the parent or legal guardian, we use a credit card as a reasonable way to ensure that you are giving us accurate information and that you are the parent or legal guardian. The following credit cards can be used: Mastercard, Visa, American Express, and Discover. You can also use a debit card with a Visa or Mastercard logo.
When you give us your credit card information, we verify that information with your bank. Yahoo! will charge you 50 cents to create a Yahoo! ID for your child. Please note that Yahoo! charges this amount to help confirm that a parent or legal guardian is involved and Yahoo! will donate a portion of that charge to charity.
This is the only means Yahoo! uses to verify that you are the parent or legal guardian, so you will be unable to create a Family Account without a valid credit card.