According to a new study, children who are unhappy are more likely to get permanently sick or disabled later in life.
For the study, researchers at the King's College London, looked at over 7,100 people born between 1950 and 1955.
They found that those described as 'miserable' or 'unhappy" by teachers were five times more likely to be off work through ill-health in middle age.
They said these kids were also likely to be more prone to depression.
The study involved thousands of children who grew up in Aberdeen in the 1950s. Teachers were asked about their temperament and school attendance.
The researchers tracked down many of the participants, now in middle age, to ask them about their employment status.
The researchers found that around 392 were unable to work because of permanent disability or ill-health, 5.5 percent of the total questioned. This could have included those retired through illness and those on incapacity benefit.
The study showed that a quarter of those whose teachers had reported them as 'often appearing miserable, unhappy, tearful or distressed' were permanently sick or disabled.
It was also found that a quarter of those who complained of aches and pain were also off sick through ill-health.
However, those who were off school because of poor physical health were no more likely to end up as adults off work sick.
"We can't say these childhood trends cause the ill-health later in life, but they certainly seem to be a contributing factor," the BBC quoted lead author Dr Max Henderson, as saying.
"Based on previous research, we suspect these groups are more susceptible to depression and anxiety, which of course is a major cause of being off work," he added.
The study has been published in the British Journal of Psychiatry.