The Best Way to Lie to a 3-Year-Old

Need to trick a 3-year-old? It's not tough, according to a new study. Just tell the kid a lie.

Three-year-olds who hear false information from an adult are more likely to believe the lies over and over again than 3-year-olds who get a false visual cue. The findings suggest that while young children can figure out duplicity, they're primed to believe things they're told.

Before the age of 4, children are extremely credulous. They accept adults' word on everything from the existence to Santa Claus to the shape of the Earth. To find out whether kids are trusting in general or whether there is something special about verbal information, University of Virginia developmental psychologist Vikram Jaswal set up two experiments.

In one, an adult showed a child two colored cups and then hid a sticker under one. The adult then told the child that if the child could find the sticker on the first try, he or she would get to keep it. Next, the adult lied to the child, saying that the sticker was under the empty cup.

The other experiment was identical, except that instead of incorrectly telling the child where the sticker was, the adult placed a black arrow on the empty cup. The children had previously played a game in which they learned that the arrow marked a cup with a toy inside.

All of the kids believed the adult on the first try for both experiments, but the kids who saw the arrow quickly caught on that they should look in the other cup. On average, those kids found the sticker about 5 out of 8 times. In contrast, the kids who heard incorrect verbal information found the sticker an average of 1.4 times. Half of them never caught on that the adult was lying to them, even after the adult reminded the kids that she'd been tricky in the past.

After the experiment, all of the kids got to keep all of the stickers, whether they'd found them or not. Kids who failed multiple times in a row were also occasionally offered a sticker to prevent frustration.

A second round of studies found that 3-year-olds who could see and hear an adult giving false information were deceived more often than children who only heard an adult's voice.

The findings suggest that kids don't have a generic trust in other people, the researchers wrote in the October issue of the journal Psychological Science. Instead, young children seem to specifically trust the testimony of others, which may stem from their dependence on adults.

"Children have developed a specific bias to believe what they're told," Jaswal said in a statement. "It's sort of a shortcut to keep them from having to evaluate what people say. It’s useful because most of the time parents and caregivers tell children things that they believe to be true."

(However, a study published last year in the Journal of Moral Education found parents lie to their children surprisingly often.)

Exactly how children become skeptical of what they're told is an area for future work, the researchers wrote.

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Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.