@Maikeru bro this report says otherwise
From Beijingwalker (Pakistan Defense Forum)
China finds 12 million children that it didn't know existed
Nov. 24 2021
BEIJING (BLOOMBERG) - China undercounted the number of children born in 2000 to 2010 by at least 11.6 million - equivalent to Belgium's current population - partly because of its stringent one-child policy.
The latest statistical yearbook released by the government puts the number of children born during that period at 172½ million, well above the 160.9 million in that age group recorded in the 2010 census.
The difference could be the result of some parents failing to register births to avoid punishment if they breached the one-child policy.
China only started
About 57 per cent of the children later registered were girls, indicating the discrepancy could be partly linked to parents not reporting girls so they could continue to try for a boy.
In addition, the 2010 census was conducted on Nov 1, 2010, so it would have missed births in the last two months of the year. Census surveys also typically do not include people who have died or emigrated in the intervening years.
The revisions show how hard it is to accurately count the number of people in the world's most populous country.