Nearly 12 million children born between 2000 and 2010 were not included in China's census. The significant undercounting of the children born during that decade was partly blamed on China's strict one-child policy.

In China's 2010 census, the government recorded around 160.9 million children born between 2000 and 2010. However, in its latest statistical yearbook, the government counted the number of children in the particular age group at 172.5 million.

Analysts said the large discrepancy could be attributed to some parents failing to properly register their additional children to avoid punishment for breaking the country's one-child policy. Before 2016, China only allowed couples to have one child.

Some parents reportedly did not officially report the birth of their second or third child, at least until they were required to register them when they turned six for school.

Given Chinese parents' preference for male offspring, some parents may not have reported girls so they could try again for a boy. The latest census showed that about 57% of the children that weren't included in the first count were girls.

The latest census survey did not include people who have died or have immigrated abroad. The revised count may have a significant margin of error given China's massive population.

Apart from the recounting of children born between 2000 and 2010, the latest census also recorded the birth rates for the years 2011 to 2017. The census revised previous numbers, suggesting that the undercounting of children may have continued after 2010.

With its declining birthrate, China has all but abandoned its previous limits on family size. Now, the country is encouraging couples to have three or more children. The government also no longer penalizes couples who exceed having three children.

Official figures show that China's birth rate dipped below 1% in 2020, marking the lowest rate of births in 43 years. According to the newly published China Statistical Yearbook 2020 issued by the National Bureau of Statistics (NBS), the birth rate in 2020 was 8.52 per thousand people.

The population's natural growth rate was 1.45 per thousand, which was likewise a 43-year low. The birth rate is the number of births divided by the total population, whereas the growth rate is the number of births minus the number of deaths.

NBS data showed that China's birth rate was 10.48 per thousand in 2019. The newest population statistics reveal the scope of China's demographic issues, which include fewer births and an aging population. The country's birth rate has been declining for years, pushing the government to modify the country's one-child policy, which had been in effect since the late 1970s.