A little boy is about to have a brother. One day the little boy walks into the bedroom, where his mother stands naked. He looks at her and ask very curious what kind of hair it is she has between her legs. The mother answers that its her flannel.
A few week later, after birth, the little boy see her naked again. When she was in the hospital the doctor shaved her which had the boy ask:
“What happened to your flannel?”

“I've lost it” The mother replied.
The little boy, who was eager to help his mother, starts looking for the flannel.

A few days passes, and the boy, yelling and screaming, burst out to his mother:
“I found your flannel, I found your flannel” The mother who suspects the boy of playing, plays along “Oh, where did you find it?”

“The nanny has it. She’s washing daddy’s face with it right now”