A little boy and a little girl are playing. The little boy pulls down his shorts and says,

A little boy and a little girl are playing. The little boy pulls down his
shorts and says, "*I* have one of these and you *don't*." The little girl
starts crying and crying and runs home to her mother.
The next day the boy and the girl are playing together again. Once again the
boy points to his private parts and says, "*I* have one of these and you
*don't*." But the little girl just keeps on playing.
"How come you're not crying today," asks the boy.
"My mother told me," says the little girl, pulling up her dress, "that with
one of *these*, I can get as many of *those* as I want."