Little Johnny sees his mother walk out of the shower and sees her vagina.
He asks her what it is and she embarassed replies, "Oh, that's mommy's black sponge."
A few days later, Johnny spills a glass of milk on the floor and says, "Mommy, I need your black sponge to mop up the milk!"
She replies, "I lost it, honey."
A couple of days later, he comes running up to her and says, "Mommy, I found your black sponge!" Mystified, she says, "Where, honey?"
Little Johnny says, "It's over at Mrs. Johnson's house, and Daddy's washing his face in it!"