5 months baby left and right leg big and small may be physiological reasons, muscle dysplasia or trauma, etc., according to the condition of the general treatment, drug treatment and surgery and other methods. 1. Physiological reasons: if the physiological causes of the left and right legs on one side of the big and small, usually do not need special treatment, as the baby grows older, the left and right legs can gradually return to normal, you can give the baby some calcium-rich food. 2. Muscle dysplasia: 5 months baby appeared the above symptoms may also be one side of the leg muscle dysplasia caused by the doctor’s guidance for the baby to take vitamin C, methylcobalamin and other drugs, can promote muscle and nerve development. 3. trauma: the situation may also be caused by trauma, parents should pay attention to timely treatment of traumatic areas, observe the baby’s recovery, usually after a period of time, the left and right legs can return to normal. 5 months baby left and right legs on one side of the big and small should go to the hospital in time to consult, choose the appropriate method of treatment.