The hard lumps in the breasts of children may be developmental, but they may also be caused by trauma or mastitis. 1. Normal development: For children with hard lumps in their breasts, it is generally considered that there may be the beginning of breast development, affected by the body’s hormones, resulting in breast lobular hyperplasia, when touched by the feeling of hard lumps, generally belong to the normal phenomenon, do not have to worry about too much. 2. Chest trauma: If a child’s chest is impacted, a local hematoma may form, and a hard lump in the mammary gland can be touched, but often accompanied by significant local pressure, it is recommended that breast ultrasound examination be carried out in a timely manner. 3. Mammary gland inflammation: If the mammary gland is ruptured or unhygienic and bacteria infect the mammary gland, mammary gland inflammation may cause hard lumps in the breast. It is recommended that children with hard lumps in their breasts go to the hospital in a timely manner, under the guidance of the doctor, according to the results of the targeted treatment, to avoid delays in the condition, resulting in other damages.