I came here to ask the same question. I installed CleanBrowsing but my son just deleted the VPN config to work around it.
He could easily remove the VPN config, access things he shouldn’t be, then add the VPN config back. I would never know.
I really like the product and was about to purchase the paid version, but then this issue came up. Any help is appreciated.
(If removal of VPN config can’t be prevented, then a feature I would suggest is to require the PIN be entered every time the Connect button is pushed in your app. That way, the kid can’t remove then add back unless they know the PIN. With that approach, I could check my son’s phone each night to make sure the VPN is still installed. If it isn’t, I take his phone away. )