Skippy arrived suddenly, when Pat’s daughter, Amy, was 4. Although he was invisible, his presence dominated family meals, where he demanded a separate place setting and minuscule but very particular helpings of food. The satisfaction of his dietary foibles was monitored by Amy with ferocious concern. “Don’t give Skippy pink ice-cream!” she would scream. “You know he only likes white!”

Witnessing this one day, I intervened: “But if you like strawberry ice-cream, Amy, why doesn’t Skippy?”

Amy gave me a withering look: “He’s not me, you know.”

Like most children’s imaginary companions (ICs), Skippy was a generally benign addition to the family. At night he happily hunkered down with Amy’s collection of stuffed toys (one of which he absolutely was not, apparently, despite being “a bit hairy”). He would take the rap for small naughtinesses, such as picking a hole in the bedroom wallpaper or leaving a toy in the rain, and so long as Skippy was with her Amy was happy to go to playschool and parties – both of which she had found scary before he came along. Sometimes, though, Amy would engage Skippy in earnest, whispered conversation, and if people tried to intervene they would be told, quite sharply, that what was being said was private. Pat started to wonder whether this was entirely normal.

It seems that she need not have worried. Children who create ICs are often assumed to be lonely or socially incompetent, and their invisible playmates are regarded by adults (if they know about them) as sad substitutes for “proper” social interaction. But now this idea appears to be wrong. Research by Dr Marjorie Taylor, a psychologist, and her colleagues at the University of Oregon suggests that it is more common today for children to have imaginary companions than not. In the 1930s, about one child in nine admitted to having an IC; by the 1990s the figure was one in three.

That number has since doubled, to more than two thirds. Furthermore, ICs seem to hang around for longer. Having an imaginary companion is at least as common among school-age children as it is among preschoolers. Far from being abnormal, the creation of ICs is beginning to look like a natural developmental process.

ICs function as playmates, confidantes and comforters. The increasing tendency of children to create them may, however, be due to something else. Children are not born with a ready-made personality, only a set of genetic dispositions that influence the extent to which they adopt or reject the characteristics they see displayed in those around them. A child who is surrounded by extroverts, for example, is likely to grow up to be extroverted, too. Children’s biggest project, therefore, is to construct what they, and others, will come to regard as their personality. To do so they pick and choose from the characteristics that they see displayed in others, trying them on for “fit” and putting some together into coherent “selves”. The process is much like putting together an outfit from a jumble of clothes and accessories.

Until a few decades ago, most children had a pretty limited “wardrobe” of characteristics from which to choose. The values, habits and perspectives of their family and neighbours may well have been the only ones they knew, and the chances were that their lives – including the characteristics they displayed as individuals – would be pretty similar to those of their parents. Now, though, children are surrounded by a dizzying variety of perspectives. In their own homes, TV and computers deliver a continuous parade of exotic characters living hugely divergent lives. Outside the home, even the smallest rural community includes people from totally different cultures. Thus children can see that there are many different ways of being, and – as they go about creating their future selves – they must pick and choose from a vast array of options.

ICs may be one way of helping children to do this because they provide additional experimental personalities. Having furnished an IC with a particular “character”, children can interact with it, and observe how this or that aspect of it goes down in the outside world before, perhaps, adopting it for themselves. Does Skippy get into trouble for not accepting pink ice-cream? Does a fibbing IC get caught out? Children can try out all sorts of behaviours vicariously, safe in the knowledge that should the IC do anything disastrous, they themselves are safe from the consequences. Older children’s ICs may be rude, rebellious or adventurous in a way that the child may not dare to be.

There is nothing essentially childlike about creating and projecting alternative selves. We do it every time that we imagine ourselves on a holiday beach, tanned and lithe, or scoring the winning point in an argument in which we were actually defeated. Unlike adults, though, children are better able to separate their fantasy self from the self in the here and now because they have yet to learn to fuse all their thoughts, feelings and actions into one, continuous, “me”.

One common way in which children reveal their lack of subjective unit is by speaking of “we” instead of “I”, or by referring to themselves in the third person. Adults are usually very quick to “correct” these errors (as they see them), and the effect of this is to encourage children to see themselves as a single self. Later, the pressure to “settle” for being one personality or another increases. “What are you going to be when you grow up?” children are asked. “Which subjects do you want to study?” “Are you mathematical or artistic?” Unacceptable or weak personalities are suffocated or sent underground.

Now we are increasingly allowed to be one thing in one situation and another in another: a pinstriped banker by day and a transvestite jazz singer at night; a mother at breakfast and a captain of industry at lunch; an IT consultant at work and a super-powered avatar in Second Life. Multiple personalities allow us to enjoy a much wider range of opportunities, and to rise to a greater variety of challenges.

Retaining the ability to create multiple selves also seems to be a signifier of artistic talent. Dr Taylor’s team interviewed 50 fiction writers – ranging from an award-winning novelist to scribblers who had never been published – and found that 46 had invented characters who had subsequently taken over the job of composing their life stories. Some of the characters also resisted their creators’ attempts to control the narrative. Some fictional folk wandered around in the writers’ houses or otherwise inhabited their everyday world.

The writers who had published their work had more frequent and detailed reports of these personalities seeming to break free of their creator’s control, suggesting that the faculty of projecting personalities into the external world really is a measure of creative expertise.

Parents who allow their children’s ICs to grow and flourish may therefore be helping their children to develop and maintain at least one form of creativity. And allowing them to “try out” various selves will give them a head start in the ever-changing and culturally diverse world that they will encounter as adults.

How to deal with your child’s IC

— Don’t be shy to interact directly with the IC if your child invites you to – it is good creative practice for you too. But allow the child to lead; if he/she wants you to acknowledge the IC, do so, but do not muscle in if the relationship between them seems to be private.

— If the IC expresses worrying sentiments – fear, say, or aggression – be aware that these may be the child’s own feelings, but do not assume that this is so.

— To find out, you might ask your child “Do you feel like XX about this, too?” or “What do you think of what XX says?” If the IC is the “vehicle” for conveying something to you that the child does not want to show directly, it may be better to deal with it by talking about it to the IC, rather than directly to the child.

— An IC should not be a child’s only playmate. Discourage your child from playing with it to the exclusion of other children.

— If an IC is aggressive or unusually anxious, be on guard for those feelings in the child and treat them appropriately.

Multiplicity: The New Science of Personality by Rita Carter, Little, Brown, £12.99

Times recommends

• Are eldest children really a cut above?
• Peaches Geldof: censored
• Top 10 style-setting films of all time