Diabetes mellitus in children is a chronic metabolic disorder characterized by persistent hyperglycemia due to defects in insulin secretion, insulin action, or both. The most common form in childhood is Type 1 diabetes mellitus, resulting from autoimmune destruction of pancreatic beta cells, leading to absolute insulin deficiency. Type 2 diabetes mellitus is increasingly observed in adolescents due to obesity and sedentary lifestyles. Early diagnosis, appropriate treatment, and long-term follow-up are essential to prevent acute and chronic complications. This article reviews the etiopathogenesis, clinical features, diagnostic criteria, differential diagnosis, treatment strategies, and medical follow-up of diabetes mellitus in children.