Level A1
Irregular plural nouns
A few nouns make the plural in their own way, with no -s: child → children, man → men, tooth → teeth, sheep → sheep.
I see two children.
Look: I see two children. Not childs: child has its own form.
Forms
one cat, two cats— usually the naming word just gets an endingone child, two children— some words have their own form for manyone man, two men— in others a sound inside the word changes: tooth, teethone sheep, two sheep— and some do not change at all
A common mistake
Wrong: I see two childs.
Right: I see two children.
So I see two childs is wrong. We say: I see two children.
More examples
My feet are cold.
Feet works the same way: My feet are cold.
Three people are waiting.
And person becomes people: Three people are waiting.