Breast pain in 7-year-old girls may be caused by trauma, precocious puberty, mastitis and other reasons. 1. trauma: trauma is usually caused by collision, extrusion and other reasons, usually lead to local soft tissue edema, lumps, pain and other symptoms, resulting in 7-year-old girls breast core pain. 2. Precocious puberty: precocious puberty is usually caused by elevated levels of sex hormones and premature secretion of gonadotropin-releasing hormone, which may lead to rapid increase in height and bone growth, and may also lead to the development of breast nucleus with pain in 7-year-old girls. 3. Mastitis: Mastitis may be caused by obstruction of milk ducts, breast trauma and other reasons, there may be breast pain, nipple inversion and other symptoms, may also trigger the symptoms of breast nucleus with pain in 7-week-old girls. It is recommended that patients seek timely medical attention to clarify the cause of the disease, and treatment is carried out under the guidance of the doctor.