On the theme of difficult ideas explained using a limited vocabulary, I suppose one has to mention xkcd's Thing Explainer as well as George Boolos's classic _Gödel's Second Incompleteness Theorem Explained in Words of One Syllable_:

https://en.wikipedia.org/wiki/Thing_Explainer

https://languagelog.ldc.upenn.edu/myl/BoolosOneSyllable.pdf