Knee pain in a 3-year-old child may be due to growing pains, calcium deficiency, trauma and other factors. 1. Growing pains: knee pain in a 3-year-old child may be related to growing pains, usually manifested as a transient, will gradually improve, does not affect daily activities, without special treatment. 2. Calcium deficiency: 3-year-olds lacking calcium or vitamin D may also experience knee pain, which may be accompanied by night terrors. 3. Trauma: knee pain in a 3-year-old child may also be related to trauma, such as bumping when playing, accompanied by bruising and other phenomena, parents should pay attention to the local skin condition. 3-year-old children knee pain may also have other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.