I think that this habit in some children is indeed one of the most disturbing. It is equally upsetting for us as parents to suspect that a child is lying but really have no way to prove what we suspect.
Certainly the age of the child makes a great deal of difference in the way that it is handled. With younger children we have to be very careful to teach the wrong of lying. It may take great patience and time to get this point across. It is important that we as parents do not allow our suspicions to override our fairness when confronted with lying. If we do not know for certain that a child is lying then it actually does more harm than good to accuse wrongly.
If it is obvious that when a child who has told a falsehood yet refuses to accept responsibility for this wrong makes our task much harder.
I think that when we speak in terms of truth and trust we are indeed getting to the real heart of the issue. As parents we must be able to trust our children in order to let them progress to greater independence. We should talk in terms of this trust and speak of it as a great privilege and priceless gift. Rebuilding trust takes time once it has been breeched.
If a child has lied and has been "caught" then it is our responsibility to be very careful in our response. Acting outraged and shocked only sends the message that we, as parents, can not be trusted to forgive and show mercy. If children feel that their "sin" is unforgivable then it only stands to reason that they will use all means to "cover up" or lie about future indiscretions. In the same respect we must enforce that the behavior of lying is unacceptable because it hurts the person who has told the lie in such deep and lasting ways.
I have worked through this with some of my own children and have tried many different methods. Please be patient when I tell you what seems to work most effectively for our family. We do not "punish" the person who has told the falsehood. We feel that the shame and embarrassment of being caught in a lie speaks to a better consequence of this behavior. When I say that we do not punish that is not to say that we just leave the problem alone. We speak in serious tones about the trust that was so easily destroyed and thrown away. We speak about the sorrow and the sadness of having had to be on the receiving end of a lie. We talk a lot about trust that must be regained at a much higher cost than the price of a simple lie.
When teens lie this is a deep, deep sorrow. We want to give them freedom to go out into the world and make choices but we do not want to risk their safety or well-being because we feel they can not be trusted.
However when we have faced the issue of lying and cover all the reasons behind the pain of this sin, then it is time to take the next step. This next step does more to "cure" lying than all the preaching and nagging. We must openly and with sincerity forgive the wrong doer and embrace their desire to regain our trust. This step is more difficult depending on the stakes in the balance. Younger children=easy; Older teens=harder.
We as parents must pray to have the wisdom of the Holy Spirit and approach this concern with care and seriousness.
Thank you for this very personal question. I think that you have touched on an issue that several families may be dealing with. With that said, remember to keep your perspective and understand that, though this is quite disturbing, it is a normal part of childhood development and needs to be approached with tender mercy and understanding and thoughtfulness.
Dearest Jesus, we ask for a special anointing upon all parents as they go about the very serious task of training up children to follow in Your will alone. Give us the empowerment of the Holy Spirit to know the words that would affect better behavior in our children. We love You, Lord, and long to see Your face. Amen.
Sending out a prayer,