China's culture (like much of asia) is heavily based on family. So I always find it interesting that they limit famalies there now. However, the average family size all over the world has been decreasing to only two children, which is why we see most of the population getting older and older (the average age of a living person). By 2100, we will see the global population stop growing as rapid as it is today, and it will reach about 10-11 billion until it stops growing all together. According to science, if we keep up the idea of a 4 person family, our world population will barely grow or shrink at that point. I reccomend watching the late Hans Rosling if you're interested.