Children lie for several reasons, whether it is because they are scared to tell the truth, or they just don't want to be punished. Your kids lying doesn't make them bad, or mean they have behavioral problems. It just makes them kids. How you deal with kids lying will determine whether or not the problem will persist.
When children are really young, they don't understand the difference between telling the truth and telling a lie. As a parent, it will be your responsibility to teach him this. Children will learn when you catch them telling a lie. Point out to your child that he just told a lie and that it is wrong to do that. Be consistent and over time, your child will learn.
Preschool children tend to stretch the truth beyond the realm of reality. They aren't intentionally lying, they just aren't able to distinguish between the truth and fantasy. When your child makes up tall tales, such as "The dragon in my room broke the lamp," point out to her that she is telling a story. Explain to her that, although it is an interesting story, it isn't the truth.
Somewhere around school age, kids lying becomes intentional. This is usually to get out of being punished for something they did wrong, such as stealing a toy or hitting a friend. Sit down with your child and tell him that what he did was wrong. Explain to him why telling the truth is important. At this age, punishing him for lying is appropriate, because he is able to tell the difference between right and wrong.
Kids lying may also be the result of being scared for doing something wrong. If your child accidentally broke a window, she may deny having done it. This would be a good time to explain that you are more upset with her lying than you are with the window being broken. The window being broken was an accident, but the lie was intentional. The truth is valued more than punishing the misbehavior.
Kids lying is sometimes an imitation of an adults behavior. When an adult tells a "white lie," children get confused. They are being told not to tell lies, but they witness you lying to someone else. White lies, such as saying you aren't home to avoid taking a call, may not seem like a big deal to you. To your child, though, it is a sign that it is okay to lie to get out of doing something you don't want to.
When it comes to kids lying, consistency is the key to dealing with it effectively. Let your child know what is expected, and lead by example. Discipline your older children when they tell a lie and reward them when they tell the truth.