Transient Synovitis: This is the most common cause of acute hip pain and limp in children, often following a viral infection. It is characterized by inflammation of the synovial membrane of the hip joint, leading to pain and limited mobility.

Idiopathic Leg Pain: Also known as "growing pains," this condition is common in children and typically presents as intermittent, bilateral leg pain, often worse at night.
Osgood-Schlatter Disease: A condition that affects the knee, causing pain and swelling below the kneecap. It is common in children during growth spurts and is related to overuse or repetitive stress on the knee.
Sever's Disease (Calcaneal Apophysitis): Inflammation of the growth plate in the heel, causing heel pain, especially in active children during periods of rapid growth.
Stress Fracture: Overuse injuries that can cause a limp, more common in children who participate in sports or repetitive activities.

Septic Arthritis: A bacterial infection within a joint, which is a medical emergency requiring prompt antibiotic treatment and possible surgical intervention to prevent long-term damage.
Slipped Capital Femoral Epiphysis (SCFE): A condition where the ball at the upper end of the femur (thigh bone) slips out of place, more common in obese or rapidly growing children. It requires urgent medical attention to prevent further complications.
Bone Tumors (e.g., Osteosarcoma, Ewing's Sarcoma): Although rare, these conditions can present with pain and a limp. Early diagnosis is crucial for effective treatment.
Child Abuse: Non-accidental trauma should always be considered in the differential diagnosis of a child presenting with a limp, especially if the history is inconsistent or there are other signs of abuse.

Legg-Calve-Perthes Disease: A rare condition where the blood supply to the ball of the hip joint is disrupted, leading to the ball's death and collapse. It typically affects children between the ages of 4 and 8.
Juvenile Idiopathic Arthritis (JIA): A chronic autoimmune disease that can cause joint pain, swelling, and stiffness. While not as common as other causes of limp, it is an important consideration in the differential diagnosis.
Neurological Conditions (e.g., Cerebral Palsy, Muscular Dystrophy): Certain neurological conditions can cause a limp due to muscle weakness or spasticity. These conditions often have other associated symptoms and signs.