Early one morning a husband and wife were doing it missionary style, when they were startled to see their 5 year old son standing by the bed.  Before they could think of something to say the littly boy yelled, "Horsey ride! Horsey ride!" and climb on his father's back.  Since they were both close to orgasm and the kid didn't know any better they continued.  It wasn't long before the wife's breathing quickened and her moans became louder.  It was then that the little boy grabbed his father around the neck and said, "Hang on tight Daddy, this is the part where me and the paperboy usually get bucked off!"