Transient Synovitis: This is a common condition in young children, often following a viral infection, characterized by inflammation of the synovial membrane of the hip joint. It typically presents with sudden onset of limp and hip pain.

Toddler's Fracture: A small fracture in one of the long bones of the leg, common in toddlers due to their developing bones and frequent falls. It can cause pain and limp.
Osteomyelitis: An infection of the bone, which can cause pain, fever, and limp in children. It's more common in younger children and can be serious if not treated promptly.
Septic Arthritis: A bacterial infection within a joint, which is a medical emergency. Symptoms include severe pain, swelling, redness, and decreased mobility of the affected joint.

Slipped Capital Femoral Epiphysis (SCFE): A condition where the ball at the upper end of the femur (thigh bone) slips out of place. It's more common in early adolescence but can occur in younger children, especially those who are overweight. If missed, it can lead to severe arthritis and mobility issues.
Child Abuse: Non-accidental trauma should always be considered in the differential diagnosis of a child presenting with unexplained injuries, including limp.
Bone Tumors: Although rare, bone tumors such as osteosarcoma or Ewing's sarcoma can present with pain and limp. Early diagnosis is crucial for effective treatment.

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 4 to 8 years old but can be seen in younger children.
Juvenile Idiopathic Arthritis (JIA): A chronic autoimmune disease that can cause joint pain and swelling, leading to limp. It's less common in very young children but should be considered in the differential diagnosis.
Neurological Conditions: Such as cerebral palsy or muscular dystrophy, which can cause gait abnormalities and limp due to muscle weakness or spasticity.