Here’s a similar question I asked a while back. Didn’t bother reading it through again though.

The majority of the population lives in rural areas and are mostly poor farmers. The more children you have, the more cheap workers you can have on the field.

Because it is an enormous, fertile land, which has been the site of thousands of years of continuous civilization. Throughout most of human history, India and China have been the most wealthy & populous regions of Earth.

I think it can be explained in mathematical terms by the doubling time formula. 70/r = n (doubling time) For instance, when r is 1 (one percent growth per year) a population will double in 70 years. China is an old culture and in there has been a lot of doubling. Currently their rate is .58% and population is 1,337,730,000. If that rate of growth hold, in 120 years, there will be nearly 2.7 billion Chinese.

The population of India is currently 1,181,348,000 but their rate of growth is 1.46%. That means there will be 3.6 billion Indians in only 44 years.

I agree with @ragingloli in that it translates into more workers in an agrarian society, but also in China there is no social security- when you can no longer work your kids can take care of you. Keep in mind that I live in the US. Anything I can say about this comes from my education, not personal experience!