Setup an account with OpenDNS, and change your router' settings to use them. But - if you are dealing with a knowledgeable teenager, he will find a way, unless you install parental monitoring app on his phone as well.
Setup an account with OpenDNS, and change your router' settings to use them. But - if you are dealing with a knowledgeable teenager, he will find a way, unless you install parental monitoring app on his phone as well.