Vasileva, M., Graf, R. K., Reinelt, T., Petermann, U., & Petermann, F. (2020). Research review: A meta‐analysis of the international prevalence and comorbidity of mental disorders in children between 1 and 7 years. Journal of Child Psychology and Psychiatry.

The epidemiology of mental health disorders in younger children has not been well studied. This review identifies an overall rate of 20% in children aged 1-7 years and the most common disorders as being any anxiety disorder, oppositional defiant disorder, attention-deficit hyperactivity disorder and depressive disorders.

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