Amazon Fire TV User Manual page 12

After you enable Parental Controls, most actions related to content viewing, purchasing, or
changing settings will require you to enter your Parental Controls PIN.
Document Update: 2014-04-02
Document ID: FTUG-2611-100
4. After you set a PIN, you can set one or more of the following settings:

Require a PIN for all purchases.

Require a PIN for Amazon Instant Video only.

Block the ability to view or purchase certain content types, such as games, apps
or photos.

Change your Parental Controls PIN.
Amazon Fire TV User Guide
Amazon Fire TV Basics
8