Children with weak knees may be related to joint sports injuries, but also due to vitamin D deficiency rickets, abnormal bone development and other reasons. 1. Joint sports injuries: some children in the usual basketball or badminton sports process, if the leg suddenly excessive external rotation knee extension or internal rotation, is likely to cause meniscus injury, especially meniscus tear injury, will appear in the knee soft phenomenon, may also be accompanied by joint popping, joint pain and other symptoms. 2. Vitamin D deficiency rickets: common in younger children, due to severe deficiency of vitamin D and calcium in the body, rickets is likely to be induced, which may cause knee weakness, may also be accompanied by excessive sweating, baldness, restless sleep and other manifestations. 3. Skeletal development abnormalities: usually due to early childhood, the child’s bone development is incomplete, resulting in skeletal deformities, such as congenital dislocation of the hip joint, flat feet, congenital clubfoot, etc., can lead to children’s weak knees. Children with weak knees may also be caused by other reasons, if the symptoms continue to fail to improve, you should seek medical attention as soon as possible to confirm the diagnosis of the cause, and then give targeted treatment.