how to block installation of applications through a web interface Google Play

[REDACTED]

I installed anti theft for my son and blocked the installation app from Goole play.
But it is useless  . Google account is of course due to the active mail and via the web he can install anything without AVAST password ...
How to set it up to him the google mail worked, but the installation was banned.

[REDACTED]

Sorry, I do not understand - how did you block installation by Google Play? Installation itself is done via Google framework (at least two or three apps and processes), you mean you used app locking to lock the Google Play? In this case you can still install the apps from internet off course.