A little girl accidentally walks in on her father while he's getting dressed.
She points to his dick and says, "Daddy, what's that?" Not wanting to explain to her yet, he says, "Uh, I can't tell you, it's a secret."
The little girl finds her mother and asks, "What is that long thing between Daddy's legs?"
Her mother also doesn't want to explain sex yet, so she says, "I don't know, he won't tell me."
A couple days later the little girl says to her mother. "Mommy, I finally figured out what that thing between Daddy's legs is. It's a toothbrush!"
"Why do you think that?" the amused mother asks.
"Because," the little girl says, "this morning I saw the maid sliding it in and out of her mouth and she had toothpaste dripping down her chin."