Twelve-year-old children with back pain may be caused by lumbar muscle strain/sprain, ankylosing spondylitis and other reasons. 1. Lumbar muscle strain/sprain: for example, excessive weight bearing, sudden external force on the lumbar region, long term heavy physical exercise or physical labor can cause strain or sprain of the lumbar muscles. This can lead to localized bruising or muscle injury, thus causing low back pain. 2. Ankylosing spondylitis: it is an autoimmune disease, which has a certain relationship with genetic factors. When the disease occurs, it can lead to pain symptoms in the muscles of the lower back. Twelve-year-old children with back pain, there may be other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.