Narrator: Who can resist an unmanned chocolate cake?
Boy 1: Shall we lick the top?
Boy 2: Yummy scrummy!
Boy 3: (laughs)
Narrator: But how best to cover your tracks?
Boy 1: Someone mysterious sneaked in when we were …
Male adult: Someone mysterious sneaked in?
Boy 4: Yeah!
Female psychologist: (laughs) Lying is a really important developmental skill. It tells us that the children can work out what's in someone else's mind in order to try and deceive them.
Boy 1: A thief came in and took that.
Boy 2: They flew down, ate it and then flew back!
Male adult: So, an elephant and a giant bird came and smudged the cake?
Boy 3: Yeah!
Narrator: To test the children's lying skills at different ages, we left them alone with a rigged gumball machine and told them not to touch it. First, we see how the four-year-olds handle the situation.
Elie: I want a sweet now.
Girl 1: Are you going to turn it?
Elie: Do you want to turn it? Turn it!
(Zoe turns the wheel)
Male psychologist: Whoa! And it's gone!
Female psychologist: Oh no! They made Zoe turn it.
Girl 1: Do not turn it any more! Nobody turn it any more, OK?
Girl 2: I just keep doing it by accident!
Female psychologist: Lying is a very subtle skill. They frequently get uncovered at this age. They haven't got the ability to problem-solve their way out of it.
Male psychologist: They're not developmentally advanced enough to lie so they tell the truth.
Female adult: What happened?!
Girl 1: It was Zoe!
Zoe: He told me to turn this thing.
Female adult: Elie, did you tell Zoe to turn it?
Elie: Well, she didn't … she … yeah, but … she listened.
Male psychologist: She listened! It was her fault for listening!
Narrator: Now it's the turn of the six-year-olds.
Children: Smarties! Sweets!
Narrator: They still turn the handle. They still gorge on sweets.
Boy 1: Yeah!
Narrator: They still panic about getting caught.
Boy 2: You guys, why did you touch that?
Narrator: But then they get rather more resourceful.
Boy 3: I've got a really, really good plan. We've got to say one lie, we've got to say one lie.
Male psychologist: This guy's worked it out that you can lie, and as long as you've got the rest of the group complicit with you (Female psychologist: OK), you get away with it.
Female adult: (surprised gasp)
Boy 4: The Smarties all came out!
Female adult: I'm getting lots of apologies but I kind of want to know what happened.
Boy 3: I was running … like this, yeah? So then we fell and banged it. So it was my fault.
Female psychologist: How ironic for parents that at the point at which their children learn to lie, they need to celebrate that as a huge developmental stage.
Male psychologist: It shows how smart the kid is, even though it also shows that you're going to be in a lot of trouble as a parent from now on.