Many factors:
I think advances in medical science and life expectancy play a large role in it. Many children would not live past childhood in the âolden days.â So it became a race against disease, Godâs will, etc. to try and have enough children so you would have some around you in your golden years. In the booming big family years of the mid 20th century, frequent pregnancies met superior healthcare and bammo â big families.
Also â the fact that women are waiting to marry and have children plays a huge role in it. The younger you are when you have your first child, the more likely youâll have many children, i.e., a big family. If you wait until youâre 34-35 to have your first child, you only have 8-10 years of fertility left, generally. And after age 35, your fertility begins a steep decline.
Finally, I think some of it is cultural. How often have you heard the phrase âmarried with 2.1 kids and a dogâ or something similar. When was the last time you heard of a grand prize was a trip for 8 to Disneyworld?
What sitcoms or other mainstream media present big families without the families being the MAIN concept of the show? (7th Heaven, 8 is enough, Cheaper by the Dozen). Itâs become an abberation.
On a side note, I think the fact that there are so few large families is a huge factor in the decline of vocations. Parents donât encourage their children to answer their call because they want their kids to have grandkids, etc. If you had 4 boys, you could âspareâ one for the priesthood.
JMO.
Laura