The sad thing about the 1 child policy is research shows you don't need to do it in an authoritarian manner to get similar results. Like in Iran, they subsidized birth control and went on an education & promotion spree and it worked too well. Iran also had a government promoted baby boom similar to what china went through also.
I was under the impression the birth rate in China was already falling quickly when the 1 child policy was introduced. That’s not to say there wasn’t abuse going on but that the over population problem was already solving itself.