How to tell if your child is lying is not always easy. But there are some tell tale signs that one can look for. The lying do not start when the talking starts. The lying starts when the child is old enough to make expressions, play act and pretend. Start paying attention to your child as early as one or two.
When my oldest son was only two years old he would hide items that he knew he was not suppose to play with behind his back when I or his dad would enter a room with him. When we walk out he would began playing with it again.
I remember one instance in particular. He did not want to go to bed. He wanted to play with his huge toy dump truck instead. We insisted and was very persistent that he go to bed. I finally got him down in bed, gave him his goodnight kiss and hug and left the room. Thirty minutes later when I went in to check on him. I found him still awake. He had put his dump truck in the bed with him. When he saw me enter the room he put that huge dump truck behind his back and just sat there in front of it and stared at me. He really thought I could not see that huge thing that extended both sides of his tiny body. When he stared at me it was like no other look he had ever given me. He looked guilty. Yes, even at two years old. I walked over to his bed, sat beside him and asked, "Wow, how did this get here. Do you know who put this here?" With no eye contact because his head was lowered, he answered in a very soft voice, "Bungee did it".
There were a couple of things wrong with this answer. First, even though he didn't speak a lot of words at this age, the few he did speak were never spoken in a soft voice. He was always loud. Second, Bungee was his stuffed bear that we named Bungee after it fell from a table and the fall was broken when he was caught in some yarn just before hitting the floor. My sister laughed at the stuffed bear and said it looked like it was bungee jumping. That is why his name was Bungee.
That was nine years ago. Today, even though he is a pretty honest kid, my eleven year old son still react the same way when he is lying. He drops his head and speaks in a very soft voice. So soft I can barely hear him. He no longer accuses Bungee, but, his ten year old brother does stand accused every now and then.
So, to tell if your child is lying or not try paying close attention to his everyday personality. Pay attention to the way he talks, his expressions, the tone of his voice and his actions and reactions to certain situations. If his pattern of expressions and reactions suddenly change he could be lying to you. It is just a matter of really knowing who your child is. As he continue to grow and develop both physically and mentally you will eventually know the difference between a lying response, a joking response, a something is wrong response, an angry response, a bored response and a I just don't care response.
There is no one simple way to know if a child is lying because each child is different. You just have to know your child.