Ouch. Hugs to ya Doc.

Anyway, the parents should have the common sense to be discreet. The child has no idea what is going on, and possibly could be a fear inducing event ("What is happening to mommy?" sort of thing). They should have the decency to wait until the child is at least asleep, and even then, be quiet. Furthermore, the child shouldn't have to watch her baby sister so her parents can take a break to have sex. That's just...wrong. :/