The paediatric idiopathic inflammatory myopathies (IIMs) are a group of rare but serious systemic autoimmune conditions of childhood. The most common of the paediatric IIMs is juvenile dermatomyositis (JDM), while polymyositis and inclusion body myositis are rare in children. JDM has a significantly different spectrum of disease from adult dermatomyositis. Juvenile myositis can also occur as part of other systemic autoimmune diseases such as scleroderma and systemic lupus erythematosus. There has recently been significant progress towards the development and validation of tools to measure disease activity and damage in the paediatric IIMs. In addition, several new therapeutic avenues have been used to treat JDM. This review will discuss developments in the diagnostic criteria for JDM, the clinical types and course of these conditions, recent progress in disease assessment, treatment options and new developments in research into the pathogenesis of paediatric IIM.