I will teach them the dangers of being online and will force the phones to use a VPN through our house with PiHole installed. I may or may not go as far as putting a custom cert on the phone so I can monitor all the traffic -- that will depend on if I catch them violating my trust. My default stance will be no custom cert.
But if I do add a custom cert it won't be a secret -- they will know that I'm monitoring them until they earn the trust back and we will review the logs together.