Growing Pains: This is the most common cause of leg pain in children, typically occurring in the calf or thigh, and is often bilateral and symmetric. It is usually worse at night and can be associated with overuse or fatigue.

Muscle Strain: Common in children who are active in sports, muscle strain can cause leg pain due to overstretching or tearing of the muscle fibers.
Shin Splints: Medial tibial stress syndrome, or shin splints, is a common condition in children who participate in running or jumping sports, causing pain in the front or side of the lower leg.
Osgood-Schlatter Disease: A condition that affects the knee, causing pain and swelling below the kneecap, typically in adolescents during growth spurts.
Juvenile Idiopathic Arthritis: An autoimmune disease that can cause joint pain and swelling, including in the legs, in children.

Septic Arthritis: A bacterial infection within a joint, which is a medical emergency requiring prompt treatment to prevent long-term damage.
Osteomyelitis: A bone infection that can cause severe leg pain, fever, and swelling, requiring immediate antibiotic treatment.
Slipped Capital Femoral Epiphysis (SCFE): A condition where the ball at the upper end of the femur slips out of place, causing hip and leg pain, which can lead to serious complications if not treated promptly.
Child Abuse: Non-accidental trauma can cause leg pain and should be considered, especially if the history is inconsistent or there are other signs of abuse.

Leukemia: Although rare, leukemia can cause bone and joint pain, including in the legs, due to the proliferation of cancer cells.
Neuroblastoma: A type of cancer that can cause leg pain if it metastasizes to the bones.
Ehlers-Danlos Syndrome: A genetic disorder that affects the body's connective tissue, potentially causing joint hypermobility and pain.
Legg-Calve-Perthes Disease: A rare condition where the blood supply to the ball of the hip joint is disrupted, causing pain and limping.