The diagnosis of O-legs in infants is made by visual observation of the lower limbs lying down with the legs together or by taking a diagnostic radiograph. When the infant is placed in the prone position with the legs straight and together, if the inner sides of the ankles are together but the inner sides of the knees are not, it can be recognized as O-legs. After the child reaches one year of age, O-legs are determined in a similar manner, except that instead of lying down, the child is placed in a standing position. X-rays can also be performed when visualization is not obvious, and the presence of O-legs can be determined by a physician’s evaluation, which can indicate the degree of inversion of the knee by the angle of the knee joint baseline to the long axis of the femur and tibia, among other things. Physiologic entropion is often present in children under 2 years of age and may improve with age. However, if infantile entropion is found to be severe, or if the deformity is still present after 2 years of age, it is recommended to go to the hospital in time for early and regular treatment.