Dear Joe,
A Gallup Poll found that in America, there was a shift, in 1971, from a family preference for four children, to a preference for two children.
The reasons: availability of birth control, increase in the number of women who work, and the increasing cost of raising children.
When most people lived in the farming environment (70% in 1920, now about 3%) children were vital because they could do some of the work necessary to farming. Now children do not contribute to the economic success of the family, as a general rule.
http://www.pewresearch.org/fact-tank/2015/05/08/ideal-size-of-the-american-family/Today, most people will either be the oldest or the youngest, since their family of origin probably consists of only two children.
As the child of parents who were both only children,I feel fortunate to have married my husband, who is the 9th of 11 children. All of his siblings had education beyond high school, and were successful and interesting people. My two children are part of 28 grandchildren, and their children have 60 second cousins.
Regards, Elaine