Block Google app on Lollipop 5.1

My son had an old Moto G running KitKat. On that phone, I set up an app locker to block the Google app because there was no way to restrict the "safe image search" on that app. Instead of him potentially being exposed to explicit images, I just blocked the app entirely. That phone broke last week, and I just bought him the new Moto G (2015). Evidently, in Lollipop, you cannot block the Google search app using an app blocker. Accordingly, there is no way to keep my son from searching for and finding explicit images using the Google search app. I have searched the internet for a solution, but cannot find one. Does anyone know whether there is any way to block the Google search app on Lollipop?