What is the reason we use plural verb with "I"?

A long time ago English verbs had a lot more endings. The "s" at the end of "eats" is one of the remaining ones. It does not signify a "singular" verb but a "third person singular" verb. It is an ending which can only be used with "he", "she", "it" or a name like "John", all of which are third person singular. "I eat " is first person singular. "You eat" is second person singular, (which, in older forms of English, would be "thou eatest").

So, you see, it would be very difficult to explain this historical English to your little pupils. Best stick with "That's how it is, kids!"

You shouldn't say that it is "the plural verb" just because it has an s on the end or whatever. Each "person" (so 'I', 'you', 'he', 'they', etc) has it own verb.

Tell them that they are lucky English is not very complicated! A lot of languages make you conjugate the endings and they are very different depending on what "person" we are talking about! Just look at any French or German conjugation chart! Even First Language Learners have trouble with them.

As has been said though, "It's just the way it is!" With languages there has been a lot of evolving and with every human language there is memorization required to learn it. :) Practice, practice, practice!

Its not a plural verb just because it ends in "s." Don't teach them that!