Little girls who play aggressive boys' games or who act out violent stories are more likely to have problems at home and at school than boys who behave in the same way.

Research based on analysing the play of five-year-old twins shows that although some aggressive behaviour is normal for boys it is more likely to indicate trouble at home and long-term behavioural problems for girls.

Child psychiatrists believe the findings, published in the Journal of the American Academy of Child and Adolescent Psychiatry, could lead to new ways of detecting and dealing with early signs of behavioural problems in young girls.

Researchers from the National Jewish Medical and Research Center, in Denver, Colorado, analysed 652 sets of twins while they were telling and acting out more than 5,000 different stories.

Dr Kim Kelsay, a psychiatrist and author of the study, said: "Children might pick up one of the dolls and smack the other or insert aggressive themes into their tales, including death and murder.

"However, when girls did tell aggressive stories, their behaviour at home and school tended to reflect it. When girls tell more aggressive stories it could be a sign of trouble". They found no such link in boys.

The researchers gave the children small plastic gender and ethnicity-specific dolls to help them create stories and gave them themes, such as discovering that the pet dog was missing, giving a gift to a parent or stealing a biscuit, and asked them to finish it in their own words and actions.

The researchers scored the children on how well their story flowed, whether it made sense and embellishments made, and levels of aggression in terms of play and words. Parents and teachers were then asked to fill out questionnaires on the children's overall behaviour.

The findings showed that generally girls had more coherent and less aggressive stories and play than boys. "Some aggression in stories is normal, but it might be more concerning when girls tell aggressive stories than when boys do," Dr Kelsay said. "Kids are working through issues in their play and if a parent senses something disturbing they shouldn't inhibit the play, but instead find out more about what's causing it."

In general, most of the children assessed did not have a clinical level of behavioural problems but Dr Kelsay found that girls with repeated aggressive and incoherent stories had more behavioural difficulties and problems than the boys who played aggressively.

Dr Sebastian Kraemer, a leading child psychiatrist from the Tavistock Clinic, London, said concern about girls' behaviour depended on the level of aggression displayed. "Our threshold for anxiety about boys' aggression is higher as we expect them to be more aggressive, hyperactive and difficult," he said.

"On its own aggression in girls is not something to worry about, but if they start torturing animals then there would be concerns. This is rather different from just playing boyish games, which is a perfectly normal thing for little girls to do."