You can always prevent unwanted or accidental purchases by adjusting password protection in the Google Play Store settings:
- Open the Google Play Store;
- Enter the 'Menu' and select 'Settings';
- Tap 'Require authentication for purchases';
- Choose one of the 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: https://support.google.com/googleplay/answer/1626831?hl=en