The official one child policy didn't actually have much of an impact. Birth rates had already fallen a lot, despite the official "lots-a-children" policy.

The one child policy is gone now but birth rates haven't really moved upwards.

It's debatable and impossible to disentangle from living standards going up, but a lot of the economy is built on assumptions of one child, from apartment sizes to personal transit (ebike can do 2 adults + 1 small child).

Not what I heard from friends who were subjected to it, and their parents.

It was insanely disruptive.

Of course it was devasting for some families. That is never the same thing as saying that it affected China's birth rate much (which it didn't).

There were forced abortions (sometimes very late), there was forced contraception, forced sterilization (I think), and lots of punishments for people who broke the policy.

There were also others who got around it fairly easily by paying a bribe and by not registering their "surplus" child/children (especially if they were girls). That of course caused some problems down the road.

That still doesn't mean that it affected China's birth rate much. It was already low (and had fallen steadily) when the policy was instituted. It also had plenty of exceptions for rural China and ethnic minorities.

Uh huh [https://en.wikipedia.org/wiki/One-child_policy]

Of course it had an impact, if nothing else, a cultural one. It basically eradicated the concept of large families.

So China has similar family sizes as the US that had no one child policy.

It's difficult to near impossible here to determine which counterfactuals would actually hold true. Based on other world wide trends it's very likely that Chinese family sizes now would only be slightly higher than if the policy didn't exist. In the modern world there are just a huge number of different factors working together to decrease family sizes.