The growing population in developing nations must be properly educated regarding schooling, jobs, & health. When those components get into place, the population will naturally decrease. When a population is educated, there is less a likelihood of them having large families. With the increase in education & jobs in developing countries, people are opting for smaller families & are using birth control.
However, there are people in postmodern nations who willfully have large/very large families. These people have an obsessive need to have children although they have been educated as to the perils, travails, & detriments of large/very large families. These people have a mindset that the more, the better although they can't possibly & efficiently raise a large number of children by themselves. Both parties have a primitive mindset & psychology. However, those in developing countries don't know any better so they have large/very large families while those who in postmodern countries really don't care, they are simply obsessed with selfishly having large/very large families. No matter how educated the latter becomes, they will persist in having large/very large families