--- - |2+ Background Research on adolescent Mental Health Literacy (MHL) is rapidly increasing; however, equivalent research in children is lacking. Exploring children's mental health conceptualisations reveals how their knowledge develops and provides the evidence base for the development of mental health education for younger age groups. Methods A total of 105 children aged 8–9 and 11–12 years were interviewed using a vignette methodology structured according to the model of illness representations, exploring: recognition, causes, consequences, timeline and curability of depression. Age, gender and experience differences were explored. Results Children were able to identify the existence of a psychological difficulty in a depressed peer; however, they struggled to categorise depression as a mental illness or to label depression. Children referred to a variety of causal factors, primarily environmental and interpersonal rather than internal biological causes. Children considered depression to be curable within a short period of 1–2 months and anticipated negative outcomes if left untreated. Older children's concepts were more sophisticated than younger children's. Gender and experience were not associated with depression concepts in this age range. Conclusions Age trends in children's mental health concepts are evident, in accordance with previous studies. Children from the age of 8–9 years demonstrate detailed concepts of depression. However, mental health educational interventions are needed to target specific gaps and misconceptions in children's understanding. - Child and Adolescent Mental Health, EarlyView.