I’m sure this is a duplicate, but I can’t find an answer on SuperUser with these words and it seems useful to at least provide a redirect.
On the Amazon Kindle Fire, how can I require that a pin number be entered for every purchase, whether it is in their appstore or in one of their games? If there isn’t a global way to do this, is there a way to secure all methods of purchasing with a pin?
The current Kindle Fire firmware supports parental controls, which when enabled requires a password to make any purchase. It is accessed from the Settings menu (gear icon at the top of the screen) then select More then Parental Controls. This function was added to Kindle Fire in an update earlier this year.
Source:
http://www.eonlinegratis.com/2013/how-can-i-lock-the-kindle-fires-app-store-to-require-a-pin-number-for-purchases/