There are multiple solutions which can be used here.
Disable or hide the app
If the device supports multi-user setup, you can can create a secondary user account for your son and put as much restrictions you want.
If you don't see Users under Settings app, your device officially doesn't support multi-user setup. See a bypass here: Multi-user option not avilable in Android one after Lollipop update
- Setup adb in PC, enable usb-debugging in device and plug the device into PC.
- Create a new user from Settings -> Users and switch to it.
- Go to Settings → Apps → All apps → find your app, tap and disable it.
If you think disabling may not be enough, simply make the app inaccessible to your son. Follow these steps:
- We need to know the UserID of the secondary user we created. For that follow my answer at How to find out currently running user name/ID from ADB?. The UserID most likely would be 10.
We're going to hide any app whose usage you find questionable for your son. Execute
adb shell pm hide --user UserID PACKAGE
Replace UserId with current user ID you found and PACKAGE with package name of the app. For Google search app, it is
Hiding here is akin to temporary removal of app, with the major difference that app is never removed from the system but only inaccessible to current user. You can always unhide the app by replacing
unhide in the said command.
You may be able to skip some steps by using Debloater app
Rely on automation
I'm not sure how your app blocker app really works. It should have no problem. Anyhow, you can use an automation app, such as Tasker to block usage of an app.
Note: some of the actions mentioned for Tasker can be achieved using MacroDroid, AutoMagic, Automate and AutomateIt individually.