Money may not buy you happiness, but having a happy childhood can make you lots of money.

A study has found that children with a sunny disposition go on to earn more as adults, even if their parents were not educated or high earners. And within the same family, it is the happiest siblings who tend to earn the most.

It will come as no surprise to self-made billionaire Sir Richard Branson, who has said in the past he was ‘extremely lucky’ to have had such a happy childhood with ‘wonderful, understanding’ parents.

The study examined the happiness levels of 90,000 children and young adults in the U.S., and compared the data to their levels of income as adults. Even when other factors were taken into account, the economists carrying out the study found that happiness levels when young clearly determined higher earnings in later life.

For example, those whose life satisfaction increased by one point on a scale of one to five at the age of 22 were likely to earn £1,200 more a year by the age of 29.

Professor Andrew Oswald of Warwick University, the study’s co-author, said: ‘This research provides yet another reason for the need to create an emotionally healthy home environment.’

Economists have long recognised that those with higher incomes tend to be happier, but this is the first study which shows the economic benefits of being happy when young.

The authors said happier people tended to be more productive which may explain why they were promoted more quickly than their more pessimistic colleagues.