If you have someone close you can trust there is probably a way to add a kiosk mode to your app and let the friend keep the password to unlock it. It could have roles about what apps, websites etc are allowed and hours.

I did very little research in it to help my brother out but I didn’t get far. I got the feeling that it’s doable even on a locked bootloader. Sorry that I don’t have more info but maybe it can set you off on the right direction.