One effective strategy for teaching preschoolers about honesty is telling or reading them stories which illustrate the power of honesty. One famous example is the story of George Washington and the cherry tree. Showing preschoolers how heroic figures told the truth may encourage them to do so as well. Also, Aesop's fables and Grimm's fairy tales illustrate the consequences of dishonesty. Such tales may likewise be effective in demonstrating the importance of honesty.
Another option for teaching preschoolers about honesty involves having them express how lying makes them feel through drawings. Conversely, ask your preschoolers to express through pictures how lying makes them feel. Divide the pictures and display them on the wall of the classroom. Ask your preschoolers to explain what they think is happening in the illustrations. Hopefully the pictures will show how lying causes pain and honesty demonstrates respect for another person.
A popular game involving lying involves one child telling a story and the other child deciding whether the story is true or false. If the child guesses right as to whether the story was true or not, then he earns a point. If the child's guess is wrong, then the storyteller gets a point. Another game involves giving a coin to a child and then closing your eyes for 10 seconds while the child passes the object to someone else. After you open your eyes, go around the room asking who has the coin. Ideally, the child who has the coin will reveal it in his hand and thus learn how to tell the truth.
If you are teaching preschoolers at a Christian school or church Sunday school, then the Bible is a useful tool in teaching your students about honesty and lying. The Book of Proverbs offers a handful of sayings about lying. The story of Abraham from the Old Testament also offers instruction about the consequences of lying.