My father has five siblings (there's more to it, but that's complicated, so let's keep to this number). And the financial conditions in the house during their growing-up years was not very good. They had a lot of difficulties. Most of the people that i know of his generation had similar situations, a large brood of children and an unstable financial condition. I still don't understand why, even after my parents and i have talked about this a few times. Yes, more children translates to more pairs of hands, more people at work and hence more money inflow into the house. However, doesn't it also mean more mouths to feed which is a tough task with insufficient money at hand? Not mentioning, sex being a taboo subject.
These days, folks of my generation are happy with a single kid. With increasing costs-of-living and the kind of money kids' require nowadays, they don't tend to think beyond two children.
There is another reason why people have more children. In the previous generation and in mine too. They don't stop reproducing (doesn't sound crude, right?) until a boy is born. We have a line of girls and then a boy.