BEING one of the ''cool kids'' could lead to children being happier and healthier than peers, a study finds.

The study of more than 300 kindergarten children found those who were in subordinate social positions were more likely to develop problematic behaviour, be depressed and perform poorly at school.

But the Californian researchers found how the children responded to their low social status could also depend on how well-off their families were.

The highest levels of ''prosocial behaviour'' - voluntary behaviour intended to benefit another child - were among lower-status children from relatively wealthy backgrounds. The children least likely to act that way were lower-status children from poor backgrounds.

Wealthy children were also generally less likely to have problems such as depression, inattention, and bad relationships and academic outcomes, although children from all backgrounds suffered the ill-effects of low status.

''Taken together, the observations presented … render even more crucial and compelling the provision, in early childhood settings, of more supportive, egalitarian, and generous social environments,'' the researchers wrote in the journal Proceedings of the National Academy of Sciences.

Jake Najman, a professor of medical sociology at the University of Queensland, said children from poorer families were starting school from a disadvantaged base.

''What they found was one of the most important determinants of the children's health was their social class or socioeconomic background,'' he said.

The children then dealt with further disadvantage at school differently because their social class affected how they learnt to interact with others. ''We know middle-class and upper-class people learn rules about how you interact that are probably more effective in terms of getting what they want,'' he said.