When I was little we called this making a rubber egg, I found it on pintrest referred to as a "naked egg" Because my boys like potty humor I asked them if they would like to make a naked egg. Of course they thought this was hilarious and wanted to know what I was talking about.
We got 4 eggs, two for each boy, and soaked them in vinegar
Immedatly the questions started "Mom what are the bubbles doing? Are they eating the shell? Is that how the egg will be naked?" I was not expecting the questions to start until the eggs were "naked" so I was very excited at their curiosity