While the One-Child Policy is administered by the Ministry of Health, it is enforced at the provincial level and experiences varied levels of enforcement. The Chinese government has used heavy fines, firing people from their jobs, and forced sterilization and abortions to keep population growth at a minimum. At this juncture, the laws have been relaxed enough where the law de facto has become a Two-Child Policy for many of the provinces. Regardless of the extent to which the laws have been relaxed, the law has been in place with enough force where it has had impact. According to the Chinese government, the have been up to 400 million prevented births due to the One-Child Policy. Setting the moral implications aside for a moment (as hard as that might be), let's ask ourselves whether it was good public policy.
Let's start with China's fertility rate. After all, it was the fear of excess population growth that triggered the One-Child Policy in the first place. Per the diagram from Pew Research [below], what we see is that the fertility peaked at about 6.0 in the mid-1960s and took a sharp decline by the late 1970s to less than 3.0, which was when Chinese government officials started to consider the One-Child Policy.
Source: Pew Research
One of the major issues with the One-Child Policy is that the Chinese government includes prevented births from the 1970s, which is 10 years before the One-Child Policy is enacted. Peer countries also had similar fertility rate declines in the latter twentieth century. As such, the vast majority of births had been averted due to a naturally declining fertility rate, not because of the One-Child Policy (Wang et al., 2013, p. 121). Even if the One-Child Policy never was enacted, China's fertility rate probably would have been around 1.5 by 2010 (ibid., p. 122). There ended up being 50 million families with only one child (ibid., p. 124). While it would be tenuous to assume that every single of those 50 million families opted for one child only because of the policy, it does at least bring the number of averted births done considerably from the commonly touted number of 400 million.
While the impact of the One-Child Policy was less minimal relative to what the Chinese government estimated, the One-Child Policy still impacted the sex ratio in China (ibid., p. 123). While part of the preference towards males is due to historical patriarchal views (e.g., ancestral worship, property inheritance), it more so has to do with the fact that sons are preferred to help maintain farmland in the rural areas. This de facto gendercide is perturbing to say the least. The United Nations Population Fund points out that while the sex ratio ticked up a little bit between 1964 and 1982 [to 109:100, which is slightly above the natural sex ratio of 105:100], the ratio was really exacerbated after the One-Child Policy took into effect. When looking at the difference between rural areas and urban areas, the sex ratio is less skewed in urban areas (i.e., the ratio is currently 112:100 in urban areas versus 119:100 in rural areas) since the incentive for son preference is smaller. I have to wonder whether the One-Child Policy has been responsible for an insanely high household savings rate [to the point where people won't spend to help boost the economy] or fewer married men resulted in higher crime rates.
Then there is the matter of the dependency ratio. By 2050, there will only be about two workers to support each retiree (Howden and Zhou, 2014, p. 19). Chinese families face the "4-2-1 dilemma" in which four grandparents are supported by two parents, and two parents supported by one child. This imbalance puts quite the pressure on younger generations to support their elders. China is facing an acute worker shortage. By 2050, it is projected by the United Nations that 13.7 percent of the population will be over 65 years of age, and only 48 percent of the population will be of working age (ibid., p. 21). This downward pressure will be felt in China's GDP growth, which the Chinese government regrettably uses as its sole metric of economic success. None of this gets into the distinct possibility that the One-Child Policy has exacerbated the female suicide rate.
Increasing fertility rates will face the uphill battles of economic development, urbanization, and cultural shifts, all of which disincentivize Chinese women to procreate. The problem is that China's fertility rate is at 1.5, which is well below replacement rates. Since countries with fertility rates below 1.5 have not been able to recover, I have to wonder if it's too late for China.
Population-boosting policies require more time for its results to take in effect, which is just another way of saying that China is an inevitable, ticking demographic time bomb waiting to happen. Demographically speaking, anything China would do to ameliorate the situation (and that includes reversing the enactment of the One-Child Policy this very second) will take at least three decades to take into effect.