Type 1 diabetes (T1DM) is an autoimmune disease with aberrant immune responses to specific β-cell autoantigens, resulting in insulin deficiency. Children and adolescents with T1DM may also develop organ-specific multiple autoimmunity in the context of APS (autoimmune polyendocrine syndrome) type 1, 2 or 3. The most frequently encountered associated autoimmune disorders in T1DM are autoimmune thyroid, followed by celiac, autoimmune gastric disease and other rare autoimmune conditions. There are limited previous studies on the prevalence of associated autoimmunity, especially multiple, in children with T1DM. The present review reports on the classification of autoimmune diabetes, and on the prevalence, pathogenesis, predictive factors and clinical presentation of pancreatic autoimmunity and of all associated autoimmune disorders in children with T1DM. The impact of associated autoimmunity on diabetes control and general health is also discussed, along with suggestions regarding screening strategies and follow-up for early detection and management of the autoimmunity.