English is hard to teach

The English language is so hard to teach. I have been trying to teach my son how to make things plural. I had to teach him that most of the time you just put an S at the end of the words. It works pretty well until he gets to words like foot. I explained that sometimes words that have a couple of Os in the middle of will turn to Es. I taught him that foot changes to feet and goose changes to geese. Then he changed moose to meese. He also changes timpani to timpanis. There is just no way to explain how things work to him. Webster was silly in his idea for having a separate English language for Americans.