“I did not have a biscuit,” says the toddler, his face the picture of innocence, despite the chocolate and crumbs smeared around his lips.

Such fibs are a universal feature of childhood; we've all told porkies, or heard them from our youngsters. But a controversial new book suggests that children start fibbing at a much younger age than previously thought, even as young as eight months old.

Published this week by Harvard University Press, How Infants Know Minds, by Vasudevi Reddy, a professor of developmental and cultural psychology at the University of Portsmouth, details how children use deception.

Reddy describes how babies as young as eight months can fake crying and laughter. She talks of nine-month-olds who, unwilling to stop playing, feign deafness despite their mothers' calls; and of babies not yet one year old acting innocent when caught doing something forbidden. By the time the children in Reddy's studies were 2 they were indulging in face-saving lies, often ready to blame siblings, to avoid punishment.

However, as familiar as Reddy's observations may seem to many of us, she is challenging the established line. The conventional view suggests that children are capable of genuine deception only once they have developed a “theory of mind”. This means they understand that people have different beliefs from their own. This develops from about four years old, and so, according to exponents of the theory, children cannot lie until that age.

Even infants try to fool their parents

The theory stems from a series of experimental tests carried out by the psychologists H. Wimmer and J. Perner in the early 1980s to see if young children could attribute a false belief to other people. But having watched more than 50 children, ranging from seven weeks old to pre-school age, in a series of studies, Reddy says her observations do not tally with the textbook view. Most of her work has involved observing infants in their homes, sometimes every week.

Last year she published her findings, Deception and Social Living, in the Royal Society journal Philosophical Transactions. From Reddy's studies, it soon became clear that infants were attempting to fool parents at a far younger age than predicted.

“We spend too much of our time treating infants as preparing to live social lives when they “grow up” rather than acknowledging that they are already living such lives now,” she says.

Reddy's work is controversial.

However, many child experts remain sceptical about her claims. Dr Richard Woolfson, a child psychologist, writer and honorary lecturer at the University of Strathclyde, believes that adults sometimes misconstrue signals.

“When a baby feigns deafness' the child is saying, 'I am concentrating on what I am doing' rather than, 'I'll pretend not to hear you'. Being egocentric, she thinks she is the centre of the world and will do what she wants.”

However, while Professor David Messer, of the Open University Centre for Childhood Development and Learning, accepts that babies do engage in “social referencing” from about nine or ten months - which means that they look to others to see how to react to events - he is not sure that this means they are capable of deception.

He does, however, support Reddy's belief that the capacity to deceive occurs at a younger age than previously thought. “Children over 16 to 18 months use pretend play, which suggests that they can distinguish between reality and pretending. There can't be a switch over at 4; it is a more gradual process.”

But why do youngsters deceive us, and should parents be worried?

Research has shown that children are rubbish liars - they succeed in convincing us less than 15 per cent of the time, and yet they persist. Reddy says this must mean that deception in babies and toddlers is not just about self-preservation or pursuit of gain. Instead, she believes they deceive to learn about the world. What starts out as a game, or a way to avoid punishment, becomes a route by which they can test which behaviours elicit approval or success and which failure or reproach.

Woolfson cautions against taking too punitive a line. Infants do not lie to be bad. They deceive to be playful or in response to an outside threat (such as a parent getting angry). That said, he says some lies should be taken seriously.

So, if your child falsely blames a sibling, Woolfson says you should calmly state: “It was not your sister. Do not do it again.” And while Reddy accepts that parents should help their children to understand the difference between truth and falsehood, she says this should not override any more immediate needs that a child may have.

Reddy's research focused mainly on infants aged six months to three years. They deceive in an attempt to engage others in emotional dialogue, says Reddy, which may take the form of getting attention, or enjoying the parents' reactions of surprise or amusement. Deception is about playfulness and social experimentation rather than anything sinister.“If the child is weaving an intricate fantasy with great seriousness, it is far more important to trust your sympathetic response and respect the fantasy than to clarify its untruth. Similarly, if the child is seeking help or attention by using some fake expression or excuse, it is likely to be more important to be sensitive to what that other need is in the child and try to meet it, than to put the child right about 'knowing the truth'.”

And she points out the importance of taking a light-hearted approach to playful tricks. “It is more important to let yourself appear to be taken by surprise than to reveal that you know the truth. The key thing is to respect the child's motivations, to enjoy their creativity and be loving in response to their needs,” she says.

And yet, reassuring as this sounds, I worry that my three-year-old son's liberal take on truthfulness could carry forward into adulthood. Reddy's views on early deception are recent<; as yet, there have been no studies exploring why some children lie but others don't, and whether those that do continue to do so when they are older. The experts say parents should not panic; children use deception to learn about the world. But if, in a few decades, I find my son in Parliament, I won't be overly surprised.

THE LOWDOWN ON ADULT LYING

Common giveaways Guarding the mouth with hand or a finger, rubbing the eye or touching the nose. Other signals that give the game away are rapid blinking, and guarded hand and arm movements. When we lie, blood rushes to the tip of the nose, causing a slight swelling - the Pinocchio effect.

Who we lie to In a University of Virginia study, 50 per cent of the students asked admitted to lying in conversations with their mothers. A survey by the website CVvalidation.com revealed that one person in three had lied on their CVs, while a 2004 survey of 5,000 women in That's Life magazine revealed that 73 per cent of women would not tell their husband if they became pregnant by someone else.

How professionals detect a liar Paul Ekman and W.V. Friesen developed a theory of emotion (Facial Action Coding System) in the 1970s, which analyses the movements of facial muscles, numbering every conceivable expression. This coding system is now used by the CIA to detect lies during questioning.

Why we lie One lie in four is designed to ease social interaction, eg, “That meal was delicious”. Another common reason for lying is to make oneself seem more interesting.

HARRIET ADDISON

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