1. Why teach it to children? I said EVEN to children. It is not good to underestimate children, and those who can understand Pythagoras can understand this perimeter classification.
2. New? New to my understanding, and to those of my friends and associates. However, such is the vastness of time and space that we cannot know whether it was discovered before, unless a student of Diophantus, or of Euclid's "Elements", or of Chinese or Indian mathematical history finds the prior art.