My father was one of 11, I am one of three. That was then. Nowadays I think 4 is a big family.
Although population growth is now being driven by longevity, rather than excess births (except in Africa). I think that, as a whole, the world has too many people in it and that optimum population, that enables, human, animal and plant life (and any other kind of life that exists) to live in harmony with other, is probably half the number we currently have and that to choose to have more than 2 children nowadays, except multiple births and one or two other rare occurences, is a little selfish and damaging to the environment.