I think that global 1 child policy would be harsh [0], though, for the lack of better term, a 'perfect' medium between 'no child at all' policy and "increase human population until it's destruction" scenario.

In perfect case couple would have up to 1 offspring, thus global medium would be something like 0.9 or 0.8, or even less. Which will reduce global population by half in 50 years.

[0] It's harsh, though would be right thing to do so we will not proliferate and consume ourselves to the point of global destruction.