A little boy caught his mom and dad having sex. After, he asked, "What were you and daddy doing?"  
The mom said, "We were baking a cake."  
A few days later, the little boy asked his mom, "Were you and daddy baking a cake in the living room?"  
She said yes, and asked him how he knew.  
He answered, "Because I licked the frosting off the couch! It was sweet!