Kindle Fire users can set Parental Controls to restrict in-app purchases. To enable Parental Controls, visit Settings (first tap More in the menu) on your device and select the Parental Controls option. On the next screen, select On located on the right side. The feature will then ask you to create a Parental Controls password that will be required to purchase any content on your Kindle Fire. Please note that once you select this setting, your password will need to be entered before every purchase.
On Kindle Fire HD, Amazons Parental Controls allow you to also set content restrictions by specifying which content types such as apps and games youd like to be blocked and made inaccessible from your device. To enable content restrictions, you must first turn Parental Controls On and then select Block and Unblock Content Types. On the next screen you can specify which content to block from your Kindle Fire HD.