You can always prevent unwanted or accidental purchases by enabling password protection in the Google Play Store settings:
- Open the Play Store app;
- Tap your account icon (upper right-hand corner of the screen) and proceed to 'Settings';
- Expand 'Authentication' and tap 'Require authentication for purchases';
- Choose one of the available options:
- For all purchases through this device on Google Play;
- Every 30 minutes.
Depending on the option selected, either all in-app purchases will require a security password or you'll need to enter a password every 30 minutes. Have a look at this article for more information.