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!
20th century, birth rates and average family sizes fell sharply, for a number of reasons including increasing costs of raising children and more women having their first child later in life. The proportion of families in the U.S. with only children increased during the Great Depression but fell during the Post–World War II baby boom. After the Korean War ended in 1953, the South Korean government suggested citizens each have one or two children to boost economic prosperity, which resulted in significantly lowered birth rates and a larger number of only children
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.