Google Android:
To prevent unwanted purchases on your Google Android device, please refer to this information from Google about requiring a password or authentication for purchases on your device: https://support.google.com/googleplay/answer/1626831?hl=en
Apple iOS:
To prevent unwanted purchases on your Apple iOS device, please refer to this information from Apple about using restrictions for purchases on your device:
https://support.apple.com/en-us/HT204396
Note: The links above take you to sites that are not created or maintained by The Pokémon Company International. We cannot guarantee results or provide troubleshooting/support for these issues.