It depends on the assumptions you're willing to make.

Imagine if Australia introduces a block that works really well, and preserves privacy, but you can bypass it by using a VPN, or by rooting your phone.

Would that be good enough, because only 1% of kids will figure out those bypasses? Or will the knowledge spread like wildfire until 90% of kids are using VPNs or rooting their phones?

If you assume such bypasses would spread like wildfire, Australia would also need to block all VPNs or make every phone impossible to root. Tough to do that in a way that isn't dystopian.