In his February, 2016 TED talk, developmental researcher Kang Lee tells us that adults cannot tell whether children are lying.
As part of his research, Dr. Lee asked children to guess the numbers on two face-down cards. The children were told that if could do that, they would get a big prize. In the middle of the game with a child, the monitor leaves the room, telling the child not to peek at the cards. Hidden cameras record the actions.
More than 90 percent of children will peek as soon as the proctor leaves the room. The more important question for Dr. Lee was when the proctor returned, would the child confess or lie about cheating? By age 4 and up, at least 80% of the children lie.
However, Dr. Lee also wanted to know if we, adults, can tell when a child is lying or telling the truth. Dr. Lee played videos of these types of games for many, many adults from all walks of life. In half of the videos, the children lied. In the other half of the videos, the children told the truth. Recognizing that if the adults guessed randomly, there would be a 50% chance of them being right, an adult whose accuracy was around 50% was a terrible detector of children’s lies.