A sudden limp in a two-year-old baby may be due to growing pains, ankle sprain, or muscle injury. According to the different causes, targeted treatment is needed. 1. Ankle sprain: children accidentally sprain the ankle joint while playing, localized edema, inflammation. Yunnan Baiyao spray can be used externally to reduce swelling and pain, can be within 72 hours of ice, 72 hours after the hot compresses to relieve symptoms, and with local braking, elevation of the affected limb. 2. Growing pains: children grow too fast, there may be calcium deficiency, and then there will be growing pains in the legs, manifested as pain in the lower limbs. Treatment is mainly calcium supplementation, can be combined with oral vitamin D, can drink more milk, and more sunshine can help relieve the symptoms. 3. Muscle injury: strenuous activities or legs suffered impact, bump, etc., muscle and local soft tissue injury, leg pain, mainly to rest. Cold compresses can be applied to the swelling within 24 hours, which can relieve the pain symptoms. If the baby limp persists, it is recommended to improve the lower limb X-ray, magnetic resonance imaging and other examinations, in order to clarify the cause of the disease and early treatment.