Writing a letter
 

There was a couple who did not want their children to know when they were going to have sex, so they decided on a code of "writing a letter."
One day, Daddy said to his daughter, "Tell your mommy that Daddy wants to write a letter." The girl went and told her mommy and the mom said, "The red ribbon is coming out, not now." The girl went back to the daddy and told him.
One day, Mommy told her daughter to tell her daddy that she wanted to write a letter. Daddy replied, "Not now. Daddy already wrote the letter by hand."