You can change your password so that you can not download anything from the store if that password is not entered before. To activate steps are:
1 -. Entering Google PlayStore choose Settings (press the menu button)
. 2 - Select and activate the "Password" option (Use password to restrict purchases)
. 4 - Confirm password of your Google account.
5 -. Displayed marked the password option and whenever you want to download something from the store will need to enter.