Background: The aim of the present study was to explore children's beliefs about the causes of psychological problems and their beliefs about potential sources of help for peers experiencing these problems. Despite its importance this is an area that has received relatively little attention from researchers. Methods: One hundred and sixteen children were read short vignettes in focus groups or individual interviews. The vignettes described the behaviour of hypothetical children with ADHD, conduct disorder and depression. Following each vignette children were asked questions about the likely causes of the behaviour and possible sources of help. A cross sectional research design was used with equal numbers of boys and girls of three age groups, the average age of the children in each group was: 8.4 years; 11.5 years and 14.3 years respectively. Results: Children of all ages were able to offer a range of explanations for the behaviour of the children described in the vignettes and these explanations varied systematically with age and the nature of the behaviour described. The majority of children believed that behaviour could change and that help to support change could be provided by family and friends. Conclusions: Results confirm and extend the findings of earlier studies that there are developmental changes in children's understanding of some common psychological problems.