As I teach my kids, I realize irregular plurals are perplexing. I came across this funny poem in Alex's English book.
One fowl is a goose, and two are called geese;
Yet the plural of moose should never be meese.
You may find a lone mouse or a whole nest of mice;
Then why can't the plural of house be hice?
We speak of a brother and also of brethren;
But though we say mother, we never say methren.
So nouns and their plurals, it's easy to see,
Make an interesting study- I think you agree.
A side note: Today I know the term brethren is antiquated. However, my children need to know that a group of Quakers are not being slandered by calling them Brethren. And when they read the KJV of the Bible they should understand that "brethern" refers to those related in the Lord.
I'm glad I'm a native speaker. Otherwise, I fear I would butcher the oxes and put the sheeps out to graze with the deers.
4 hours ago