Familly sharing - How to let a child download an app without entering his itunes password?

My child is connected to me with familly sharing in iOS 8.

However he still needs to enter the itunes password when choosing an App in the app store. Is it possible to switch this off?

I don't want to give him his itunes password because then he can change his age to an age over 18. In this way he can use my visa without my agreement and change other settings.