I would remind everyone that the ban of porn below 18 is not enforced, but it is enough to ensure it is not consumed openly or at school. That is how this will play out too.
Kids also find alcohol. Can't supply as an adult or company.
The problem for the social media companies is that their recommendation algorithms and content make it very clear they know exactly what ages are watching and what they are showing them. They are multi-billion dollar multi-national operations and not some kid running an iffy image board. I usually hate the Australian government's dumb takes on anything tech or Internet (cryptography, internet filters) but in this case I think pushing regulatory compliance on large companies is what makes this doable.