Hemarthrosis: This condition, characterized by bleeding into the joint space, is a common complication in patients with hemophilia. The hip joint is a frequent site for hemarthrosis, and it can occur spontaneously without any preceding trauma. The acute onset of hip pain in a child with hemophilia strongly suggests this diagnosis.

Septic Arthritis: Although less common than hemarthrosis in this context, septic arthritis is a significant concern in any child presenting with acute hip pain, especially if there's an underlying condition like hemophilia that might predispose to infections.
Osteonecrosis (Avascular Necrosis): This condition can occur in patients with hemophilia due to recurrent bleeding into the joint, leading to damage of the blood supply to the bone. It might not be the immediate cause of acute pain but could be a contributing factor in the context of chronic joint disease.
Musculoskeletal Strain: Though less likely given the absence of trauma, musculoskeletal strains or overuse injuries could potentially cause hip pain in an active child.

Slipped Capital Femoral Epiphysis (SCFE): This is a serious condition that requires prompt diagnosis and treatment to avoid long-term consequences. It can present with hip pain and is more common in obese children or those with certain medical conditions, but it should be considered in any child with acute hip pain.
Bone Tumor: Although rare, a bone tumor could cause hip pain. Given the potential severity of this diagnosis, it's crucial not to miss it, even if it's unlikely.
Infectious Diseases (e.g., Osteomyelitis): Infections of the bone or surrounding tissues can cause severe pain and have serious consequences if not treated promptly.

Legg-Calve-Perthes Disease: This condition involves avascular necrosis of the femoral head but typically presents in a slightly older age group and might not be as directly associated with hemophilia as other forms of osteonecrosis.
Transient Synovitis: This condition can cause hip pain in children but is more common in the context of a recent viral infection and might not be as strongly associated with hemophilia.
Gaucher Disease: A rare genetic disorder that can cause bone pain and might be associated with hemophilia in some cases, though it's less directly related to acute hip pain without other systemic symptoms.