If your children or other underage relatives shop in the iTunes Store, you can limit their usage of your credit card by setting up iTunes Allowance for their iTunes Store account. Follow these steps:
1. Sign in to the iTunes Store.
2. Go the the Set up an iTunes Allowance page.
3. Fill in the form with the following info:
• Your name that will appear in the message to the person for which you create the Allowance.
• Your recipient's name.
• Dollar amount for the allowance that will be withdrawn from your credit card each month.
• The month from which the allowance will come into force.
• Your recipient's Apple ID (if they don’t have one, you can instantly create a new account for them).
• Personal message for the recipient.
4. Confirm the accuracy of the data you’ve entered.