Don't let kids have an internet-connected phone, the same way they can't have a bottle of wine.
If they really need such device make sure that device is locked to a small list of app/contacts possible.
There's no need to lock down the rest of the internet because the responsible person of such kid can't tolerate their complaints. It is a parenting issue.
Unless your point was that we should legally ban kids from handling phones, which I think is too extreme.
Chase the responsible adult if you see a kid with an overpowered phone, much like you would if you found the same kid with a bottle of wine.
And granted, we don't have locked-enough phone in market yet, but that's a solvable problem if we were to create that market.
I have seen religious parents been vocally opposed to their children seeing or even discussing anything related to sexuality.
An example from the past:
"The National Legion of Decency, also known as the Catholic Legion of Decency, was an American Catholic group founded in 1934 by the Archbishop of Cincinnati, John T. McNicholas, as an organization dedicated to identifying objectionable content in motion pictures on behalf of Catholic audiences."
https://en.wikipedia.org/wiki/Legion_of_Decency
https://www.archbalt.org/catholicism-influenced-moviemaking-...