This is David Brooks:
If you want to summarize the changes in family structure over the past century, the truest thing to say is this: We’ve made life freer for individuals and more unstable for families. We’ve made life better for adults but worse for children. We’ve moved from big, interconnected, and extended families, which helped protect the most vulnerable people in society from the shocks of life, to smaller, detached nuclear families (a married couple and their children), which give the most privileged people in society room to maximize their talents and expand their options. The shift from bigger and interconnected extended families to smaller and detached nuclear families ultimately led to a familial system that liberates the rich and ravages the working-class and the poor.
This is interesting but also somewhat naive. Going back generations, families lived in close proximity as large groups because they were likely engaged in agriculture. Also, transportation was not convenient so there was little reason to move too far away from home. Sons helped on the farm until they could buy parcels of land of their own. Daughters married into neighboring families. Infant mortality was relatively high. People were unlikely to survive long into retirement. There was no old age retirement security, so the kids took care of Mom and worked her land. It wasn’t so much of a family structure than an agrarian arrangement. This began to change as the proportion of people living on farms diminished. The way this worked was kids of farmers would leave for college and never return. With each generation farms would become larger and fewer and fewer people remained to work them.