Make telling the truth easier than lying
All children lie from time to time. But honesty is a key part of good character. If your child has told you a lie, talk together about the consequences of dishonesty. "When you tell me you've done your schoolwork and I find out you haven't, it makes me wonder whether I can trust you." Also make sure you aren't providing chances to lie: If you know your child spilled the milk, ask, "How did it spill?" not, "Did you spill the milk?"