The most common cause of hard bumps behind a child’s ear is an enlarged lymph node behind the ear, which can also be caused by a sebaceous cyst. If the small hard bags behind a child’s ear are round or oval peanut or soybean size, and the mobility is relatively good, with a finger gently pushed can feel the small bag inside the sliding, this situation may be lymph node enlargement. If the texture of the small hard bag is slightly soft, the mobility is relatively poor, and it does not hurt or itch when you touch it, this is usually a subcutaneous cyst caused by a blockage of the sebaceous gland ducts in the skin behind the ear. These subcutaneous cysts are generally benign, and as long as they are handled properly, they are not harmful to your health, so don’t worry too much. If a small hard bag appears behind the child’s ear, it is recommended to consult a doctor in time, conduct relevant examinations, clearly diagnose the cause of the disease, and then carry out targeted treatment to avoid aggravation of the condition.