Years ago, my friend Andrea had a saying about unkind words: "Words are like toothpaste...Once they come out you can't put them back!" I came across a children's sermon about that very same idea!
Title: The Power of Words
Source: Object Lessons for a Year by David Claassen
Scripture Reference: Col.3:17
Supplies Needed: A tube of toothpaste and a paper plate
Lesson: (see link)