As someone who lived through the Cuban missile crisis, and can remember the weekly (in our case Friday at noon) air raid warnings, and the duck and cover training at school, this was a real threat.
WWII was less than 20 years in the past.
The Soviet Union was a real threat.
Would air raid shelters actually work, most likely not since they did not take into account what you do when the attack is over. But that is not how you have to look at it.
People were scared. What could a father do to protect their families. This was one option.
I go back further,,,, into the 50s for grade school. I remember the” get under your desk and cover your neck with your hands” drills.
Remember Cuban Missile Crisis - was in 2nd grade
Rumor was that Russkies had targeted the school
Thought that was pretty cool - would not have to go to school......