Kids in schools which forbid phone use for everyone are often happy with the result. Banning social networks for everyone may be popular with them by the time they vote.

What about the 14-15 year olds who happily use who happily use various apps to keep in touch with their family and friends (outside school hours), who will now be prohibited from doing so?

You don't need social networks to keep in touch with family and friends. RCS and a large number of communicators are available for everyone.

Postal mail is also available to everyone, but it's as functionally equivalent to Instagram as RCS is.

"I want Instagram" and "I want to be in touch with my friends and family" are completely separate things. You don't need social networks for that. It was possible to be in touch before the internet and I believe that Instagram didn't improve it at all.

By that logic, we could simply ban the internet and save a lot of trouble. Society functioned without it for thousands of years.

Why go to extremes? The internet does improve the friends&family communication a lot and is useful. I'm saying that Instagram and other social media don't improve it that much beyond direct communication.

I'm not Australian, how are they now being prohibited?

They don't really have a plan yet.

Thinking things through isn't a quality that Australian governments have ever been blessed with, particularly when it comes to tech policy.

This will be wholly supported by both parties of our primarily two-party system. There's no alternative but a protest vote to one of those fringe parties that will never get any real power anyway.

A protest vote is still free in Australia due to a reasonable voting system. And quite a few independents still get in. Is not terrible and actually can make a difference.