Many devices come with the option of protecting your purchases by requiring a password when a purchase is made. 

 

This behavior can also often be customized by, for example, removing the ability to make any in-app purchases, requiring a password for every purchase or requiring a password for every purchase outside of a  given time frame.

 

With an Android based device you can also setup new user profiles and alter the settings for each profile. Parental/payment settings will vary by device and OS, please check the following articles for more details:

 

• Payment authentication for Google Play.
• Payment authentication for iOS devices.