Newborn baby legs are bent is a physiological phenomenon. Because under normal circumstances, a healthy newborn after delivery of the limbs there is muscle tension, so the legs are naturally flexed, even if the artificial force to straighten the child’s legs, calves may not be straight, more or less have some arc. However, the child should be supplemented with vitamin D3 every day from the 15th day after birth for the prevention of vitamin D deficiency rickets. If the child is not supplemented in time, it is easy to cause vitamin D deficiency, the symptoms of O-shaped legs, X-shaped legs, manifested in the legs of the inner edge of the inner ankle or the inner edge of the inner knee when standing naturally is greater than 3cm, this situation is a pathological symptom that requires drug treatment.