I'm an only child; I never had siblings.
You must have been lonely growing up!  What did you do for companionship?
The proportion of families in the US with only children fell during Post-WW2 baby boom, but I guess I'm a Gen X kid.  Oh, I had imaginary friends!
So before WW2 there were many families with only one child?  That's sad.  Thank goodness for the baby boom!
Oh that was due to the Great Depression.  People couldn't afford to have kids!
That makes sense - The Great Depression must have been a bad time to live in, and I bet people were relieved when it ended!
New Deal
The New Deal was a series of programs, public work projects, financial reforms, and regulations enacted by President Franklin D. Roosevelt in the United States between 1933 and 1936. It responded to needs for relief, reform, and recovery from the Great Depression. Major federal programs included the Civilian Conservation Corps (CCC), the Civil Works Administration (CWA), the Farm Security Administration (FSA), the National Industrial Recovery Act of 1933 (NIRA) and the Social Security Administration (SSA). They
and WW2 Government Code and Cypher School.
During World War I he had been elected Librarian at King's College, but never took up the appointment. After the war Knox intended to resume his research at King’s, but was persuaded by his wife to remain at his secret work; indeed, so secret was this work that his own children had no idea, until many years after his death, what he did for a living, and his contribution to the war effort.
Codebreaking Between WW1 and WW2 Commercial Enigma.