Why has my child been charged $1.00 by iTunes?
iTunes often tests that a card is valid by making a small transaction first. This is sometimes done when an online order is placed or when setting up a new account.
These transactions temporarily block these funds and your son or daughter will get the money back within 10 days. Your children will need to make sure this amount of money is also available when they place an order with iTunes otherwise the transaction might not go through.
For instance, if the app they want to buy costs $2.99 they will need to make sure they have $3.99 in their account to complete the purchase.