We do not store your credit card number or your credit card expiration date. We only know the last-4 digits of your card number once used. We have a different way to charge your card for renewals and subsequent purchases.
Your information is only visible to you, or to other members of your family of accounts. In order to protect your card from misuse, only the Family Master account may make charges if you've setup a family account.
To protect a card from re-use by a child, the parent is able to setup a "Parental Control" password on the account. This is merely a secondary password that is needed in order to make purchases, or make certain permissions changes in the account. The idea is that a child may have a Wizard101 account of their own, but the parent can control their access levels (such as ability to use Filtered Chat, or Friends Chat) within the game, and the parent can control when purchases are made against the account. The parent will also get a copy (CC) on any emails sent to the child - to assure that the parent is aware of any messages from the game that the child receives.
With Parental Controls, the child does not need to know the parent's password in order to play the game, or login to the website. But the child cannot make changes to the account's permissions or make purchases unless they also supply the parent control password.