why don't you whisper

A mother took her little boy to church. While in church the little boy said : “Mommy, I have to pee.” .
The mother said to the little boy, “It’s not appropriate to say the word "pee" in church. From now on when you have to "pee" just tell me that you have to whisper.”
The following Sunday, the little boy went to church with his father and during the service said to his father:
“Daddy, I have to whisper.”
The father looked at him and said, 
“Okay, why don’t you whisper in my ear.”