Casts are widely used for traumatic injuries and various musculoskeletal disorders in orthopaedic practice. It is also used for pediatric fractures usually. Casts can be applied to provide immobilization for nondisplaced fractures, reduce the displacement in fractures, and protect the operated fracture. In this review, the fundamental principles and applications of pediatric casts are discussed. Humeral shaft fractures consist 1% of all fractures. These fractures occur in commonplace falls, traffic accidents, and sports injuries. Good and excellent fracture healing, and satisfactory functional results are reported in the conservative treatment of humeral shaft fractures. In this review, the technique and principles of hanging cast, U splint, and functional brace are discussed.