Leg pain in 4-year-old children may be caused by trauma, growing pains, hip dysplasia and other factors. 1. trauma: after strenuous exercise, the ligaments or muscles of the legs are easily damaged, making the child suffer from leg pain. 2. Growing pains: Growing pains is a common condition in children under 13 years old, which is characterized by pain in the thighs, calves, knees and other parts of the body, which can be relieved by massaging the legs or applying hot compresses on the painful parts. 3. Hip dysplasia: Hip dysplasia may be related to heredity, abnormal fetal position and other factors, manifesting as hip pain, limping when walking, etc. It can be improved through reset treatment and femoral epiphyseal drilling. If the symptoms of leg pain are more serious, you should take your child to the hospital in time to check the cause of the leg pain, and use the appropriate treatment under the guidance of the doctor.