I read that if they did this today, it wouldn't make a difference, it's too late to recover from now, mathematical impossibility.
The majority of their population is beyond the child bearing age so it's downhill from here no matter what policies they put in place, there's going to be a major population crash for them in the next 30 years.
Since we're talking about an amoral baby making law, the age bracket 16-36 is more realistic. Doesn't change much in terms of population, but also doesn't explain how it will be enforced.
However this is just the beginning. After that, assuming worst case labour practices, you have another 10-15 years of supporting increasingly expensive unproductive citizens before they can even start to pay back the costs on society they incurred by being born. It's a long slow road...
As usual Neal Stephenson was ahead of the game. The plot to duplicate "A Young Lady's Illustrated Primer" is facilitated by Confucians needing educational materials for vast numbers of girls (maybe clones?) being raised on nursery ships.
So roughly 20 years from now, after taking on a country-wide new baby-boom's worth of problems, they can use the fresh faces to resolve the problems they're facing today.
How the one child policy was allowed to happen is a mystery to me - surely someone saw this coming?
We need to accept this and start immediately facing it head on. I'm talking a 5 Trillion Dollar investment into manufacturing in the US. Set a goal of 5 years. After that 5 years we cease any and all import from China and countries beholden to them.
While extracting and exporting every ounce of oil the US has. The profit made goes into Nuclear and Renewable Energy.
Next we Annex Canada and Mexico to further build out US infrastructure. We will dub this the Nation of North America.
https://en.wikipedia.org/wiki/Demographics_of_China