M, S and I are in the car.
M: Mommy, are mouses very small?
MV, employing the universally agreed-upon technique in language pedagogy, gentle correction by example: Yes, M, mice are very small.
M: Thank you, but I was asking about mouses.
S takes over: M, there's no such thing as mouses. When you're talking about more than one mouse, you say mice. That's just the word, that's the way it is.
A long silence
M: Is there such a thing as "rats"?