For your amusement: "Duck and cover" school video from 1951
Want a hilarious blast from the past? The Internet Archive hosts this video on "Duck and Cover", a production of the Department of Defense meant to teach kids what to do in case of an atomic attack. The video focuses on Bert the Turtle, who retreats into his shell whenever a monkey tries to explode a stick of TNT next to his head. (Uhhhh...) The narrator pulls out all the stops in scaring the bejeezus out of kids, explaining that the nuclear air raid alarms can sound "at any time, even when you're outside playing". Hell, an attack can even come so quickly that there will be no air raid siren! One scene shows two kids, Paul and Patty, walking to school as the narrator outlines the potential doom they face: "Here they are going to school on a beautiful spring day...but no matter where they go or what they do, they always try to remember what to do if the atom bomb explodes right then. [White flash] It's a bomb! Duck, and cover!"
It's amazing any child of that era was able to sleep at night.
Perhaps the most surprising thing about this video is that, despite having been produced in 1951, it depicts a racially integrated classroom. I imagine this reel didn't get much play in the South...
Start by teaching him that it is safe to do so.