Perhaps not a quota, but maybe no subsidies/tax cuts for babies!

Yes - get rid of the "baby bonus" etc - thats fine.

IIRC our birth rate is under replacement rate anyway, so if you wanted to stabilise Australia's population, the easy way to do it is to cut immigration back to the appropriate level.

And if you want to stabilise the world's population, you'd fund efforts in the developing world to improve women's education, give them access to contraception and to become economically independent - which are the most effective ways of achieving a manageable birth rate.

I've always thought that there was something strange about promoting "Australian Babies" instead of upping the immigration intake if the objective was population growth...

The other measures you mention are known to produce (or are at least correlated with)lower birth rates... and these measure are sadly resisted for that very reason, by those with other agendas/ideas.