Why were families larger in the past than nowadays?

In the past, women had five or six children on average, though many babies died soon after birth or in their infancy. For example, in the eighteenth century in France, half of all children died before age ten, and only one-third reached adulthood. Parents had lots of children to ensure that at least some of them survived. Today, child mortality is much lower and in many countries the death of a child is a rare event. Children are practically certain to grow up, so parents no longer need to raise large families. Parents also choose to have smaller families because they want to give their children every opportunity for a better life. This means providing education, land, capital etc. But parents’ assets are limited, and when they are shared between many children, the amount each one receives is small. Hence the preference for a smaller number of children, each better equipped to make a good start in life.

Source : Pour les données de 2011 : Couples et familles, Insee Références, Édition 2015

Update : 6/15/2017