Do you choose to be stupid? Or were you born like this? You know exactly what OP meant, if you can't have a proper discussion, feel free to use your half braincell somewhere else.
@OP: I think it's unusual for parents to have sex when the kids are around. I'd hope that they make sure the kids are asleep if the parents are about to have sex. Also, I'd think that it's better to talk to your kids about the topic instead of carelessly having sex around kids.
Jesus christ, are you for real? xD