Nine-year-old children leg pain may be related to muscle spasm, tibial tuberosity epiphysitis, calcium deficiency and so on. 1. Muscle spasms: small children sleeping at night without covers, leg muscles are stimulated by cold, causing local muscle spasms, which can lead to nine-year-old children leg pain. 2. Tibial tuberosity epiphysitis: it may be related to hormones, nutritional supply, trauma, genetics and other factors. In the process of bone growth and development, the bone density increases in some parts of the bone, and the center of ossification appears irregular and broken, usually accompanied by leg pain. 3. Calcium deficiency: when the balance of calcium in muscles is disrupted, it will cause pain, twitching and decreased function of skeletal muscles, so leg pain will occur. Leg pain in a nine-year-old child can also be seen in other causes, it is recommended to consult a doctor in a timely manner, follow the doctor’s instructions for relevant examinations, with the help of the doctor to clarify the cause, and targeted treatment or therapy.