I remember learning this phrase from the Little House books. It basically means that adults should be careful about what they say within the hearing of children. I came across an interesting video and article that shows this is so true, even at a very early age. Researchers at the University of Washington have found that toddlers change their behavior to avoid making grown-ups angry. If you've had a toddler, you may not fully believe that could be true, but watch the video and see!