Children commonly lie to try to escape punishment. Hence the saying, "Ask me no questions and I'll tell you no lies." These are called self-protective lies. During the first 5 or 6 years of life, children go through a normal phase of trying to cover up by lying. They stop lying when they learn it doesn't convince anyone.
"Don't lie. Tell me the truth."
If your child lies, respond as follows:
Praise your child for telling the truth.
Be truthful yourself and lie as little as possible (including tactful lies).