Children may lie because they cannot think of any other way of handling a situation without hurting themselves or someone else.
What to do to stop that?
Let your child know that you take lying seriously.
Help him understand the negative consequences of lying in ways that are appropriate for his age
Think of yourself as a teacher instead of a police officer.You should know that teaching takes time. Consistency is important, and it will take time for him to consistently tell the truth.
If your child has, for example, stolen a friend's toy and told you it was a gift, do not focus exclusively on the lie when you talk to your child. Instead, focus on the stealing, which was the child's behavior that led up to the lie.
Make it very easy for your child to tell the truth and give him a chance to confess. Don’t stage a courtroom drama and try to force a confession.
Respect your child privacy, so he doesn't need to lie to protect his privacy.
If lying becomes a habit, some parents may purchase a small journal in which to write down each incident of lying. The purpose of the journal keeping is that it is a visual aid for how often lying is occurring. Are there certain persons that are lied to more often than others? Demonstrate to the child in a neutral tone the number of times you know they have lied. Do some role-playing with your children, on how to get out of awkward social situations.
Finally show love. Love has a way of mending broken trust issues that no psychologist or discipline can touch. The gift of love is truth telling at its finest. Share it with your children freely and without measure.