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!
The 1930s was one time when government intervention was very helpful, with the passing of entitlement programs in the New Deal.  Things like Social Security, and Farm Security Administration.