act out the singular and plural aspect. He, she, and it with students and something very funny. Then the plural forms in the same way. Try to make it into a chant or a game to confuse them. In the end if you can get across the idea of one in singular. Anymore than that is plural. Act it all out. Then they can see, hear, and experience what is happening.
Use a variety of fun verbs that fit the context of the lesson and joke you are heading for.