The possible causes of sudden knee pain in children include growing pains, trauma, septic osteomyelitis or arthritis. 1. Growing pains: growing pains refers to a physiological pain in the lower limbs of children, which may be associated with a greater amount of pediatric exercise, growth and development process of the long bones grow too fast, the growth of local muscle ligaments are not coordinated and other factors, characterized by pain in the lower limbs in addition to more than no other manifestations. 2. Trauma: children’s activities are more exuberant, easy to be injured and cause knee pain, children usually have a clear history of trauma, local redness, swelling, ecchymosis, pressure and pain and other manifestations. 3. Purulent osteomyelitis or arthritis: Purulent osteomyelitis or arthritis is an infectious inflammation of the bone and joint system, mostly seen in children and adolescents, children mainly manifested as severe local pain, unwilling to move the affected limbs, examination can be found in the local muscle spasm, with deep pressure pain. Children often have high fever, chills, chills and other systemic manifestations of infection. Children suddenly knee 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.