Changing Purchasing Permissions

You can manage your son's permissions via the Family Settings. Follow the steps below:

• On the My Xbox row, scroll to the right.
• Select Family Settings.
• Select the Avatar of the child account you wish to modify. 
• Scroll right twice to the Online Safety tab and select Change Settings.
• Select Customize.
• Under Activity select Purchase Content.
• Select Blocked.

This will block the account from purchasing Premium Content (arcade games, add-ons, etc). Free content will still be allowed as determined by the content settings that are in place. Try this out and see if it prevents you from attempting to purchase content (you don't have to complete the purchase, just hit the Buy button once to get to the confirmation screen).

As a precaution, since you're concerned about further charges, if you submitted payment with a credit card there will be a forced automatic renewal option. Although some sources say you can remove this online - that feature is broken and the only current way to remove this is by calling their support at: Toll free: (800) 4MY-XBOX or (800) 469-9269

If you opt not to cancel the auto-renew, by the time you see the charge on your bank account it may be too late to request a refund. (For myself it wasn't charged until 30 days after the 'billing date')

If you do opt to call them to cancel the auto-renew be sure to have the information listed from this page handy: support.xbox.com/.../call-us.aspx

Hope everything works out!