And all other parts of this are very, very stupid too.

At hardly any prior time have children/teenagers been such a small share of the population of western countries as they are now. So whatever problems there are that concern children/teenagers, they are much less relevant than they may once have been.

Mainstream social media is ultimately part of the advertising industry. Minors generally don't have a lot of money to spend on anything advertised on it; so social media companies don't have a single rational reason to target minors especially more than adults. Minors are one of the least lucrative advertising targets in the world.