***makes sense to concentrate on quality over quantity.***
Yet the real reason for having many children at that time was that most of them would not make it to adulthood.
Most would die as children. Some would make it to the teen years. One or two might make it to old age and have families.
There is a story about a doctor who went into the jungles somewhere and gave the children innoclulations against diseases.
When he told the tribal elders how this would allow the children to live to old age, they said ....It was good, but who would feed them?
Such a story may exist "out there" somewhere, but it doesn't make sense in the context of the life realities of primitive people.
Human grouips living at a subsistence level do not make distinctions betweel "producers" and "consumers," because almost everybody at every age is both. A 4-year-old can gather aticks to make a fire and can watch that his younger siblings don't wander off. A 6-year-old can pick up nuts and pick berries and gather eggs and follow fairly complex instructions from his elders. By age 8 a child can be efficient enough to be a net surplus producer, and thereafter extremely valuable from an economic standpoint, especially if his parents or grandparents are ill or injured or otherwise impaired.
This is true in hunter-gatherer, herder-nomad and farming societies alike. The poorer you are, the less you can afford the luxury of NOT investing heavily in children.
And yes, many pre-modern societies had a high mortality rate balanced by a high natality rate: but all of them reckoned children as wealth.
We'll earn that lesson painfully but well between now and 2015.