A couple in the bedroom and the children

A couple found themselves feeling a little "frisky" so they sent the children outside to play, went into the bedroom, and locked the door. After a while, the older boy grew tired of playing and came into the house. He noticed odd noises coming from his parents' bedroom and went over and spied through the keyhole. He ran out to get his sister, brought her inside and told her to look. As she looked through the slot in the door, she said "Oh, sure, this from the woman who tells me not to suck my thumb!"