Two and a half year old babies say leg pain has physiological factors, may also be muscle strain, osteosarcoma and other pathological factors. 1. Physiological factors: children due to the motor system is still in development, two and a half year old babies will have leg pain after too much fatigue, physiological factors lead to leg pain usually after a period of time can be recovered on their own. 2. Pathological factors: (1) muscle strain: two and a half year old babies are in the naughty stage, love to run and jump, if long time running and jumping may cause local muscle strain resulting in leg pain. (2) Osteosarcoma: Osteosarcoma is one of the most common bone malignant tumors, which develops from mesenchymal cell lines and manifests itself in pain, lumps, and walking limp. Two and a half year old baby said leg pain may also have other reasons, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.