All parents tell their children little white lies from time to time. ‘Of course Father Christmas comes down the chimney!’ ‘Eat your spinach — you’ll get as strong as Popeye.’ ‘No, I didn’t put that pound under your pillow. It was the Tooth Fairy,’ ... and so on. It’s all part of the magic of childhood.

However, there’s one fib that’s bigger than all the others. It’s ‘I don’t have a favourite child.’

In his fascinating new book, The Sibling Effect: What Bonds Among Brothers and Sisters Reveal About Us, Jeffrey Kluger, a father of two daughters, aged eight and ten, claims that ‘95 percent of parents in the world have a favourite child — and the other 5 percent are lying.’

Kluger may be exaggerating the figures for dramatic effect — but despite every parent’s vehement denial that they have a favourite child — scientific research shows that he is not far off the truth.

According to one recent study by researchers from the University of California — which followed 384 sibling pairs and their parents for three years — 65 percent of the mothers and 70 percent of fathers exhibited a preference for one child. As this was among families that knew they were being monitored, there’s a strong possibility the true figures could be significantly higher.

Favouritism is certainly a controversial topic. When raised as a subject for discussion on parenting websites, it always elicits a stream of outrage and angry denials.

But interestingly, a lot of personal anecdotes appear from parents who say they were overshadowed by a favoured sibling, or were, indeed, their mother or father’s favourite. It seems everyone knows favouritism exists — but nobody wants to put their hand up and say they’re guilty of it themselves.

Other research, where siblings have been asked to say who their mother and father favour, suggests that mothers do tend to a show a preference for their first-born son, but fathers often dote on their youngest daughters.

Parents will often be drawn to the child who is easiest to get along with — or the child that shares similar traits to them. For example, mum will have a special bond with her sensitive, arty son, while dad lavishes attention on his sporty daughter.

Professor Scott says being least favoured in a family can colour our behaviour as adults. ‘Children who feel they are less loved within their family are more likely to develop low self-esteem, anxiety and depression.’

But some experts believe being less favoured can have positive consequences. Professor Scott agrees that favoured children can sometimes find life difficult when they have to rub along in the real world.