Hard lumps on the left side below the belly button in children may be caused by fecal mass due to indigestion, etc. They may also be caused by tumors on the left side of the abdomen and inguinal hernia. 1. Fecal mass: children due to indigestion and constipation lead to fecal stagnation in the intestinal tract, forming a huge fecal mass in the left lower abdomen. A hard lump can be felt on the left side below the navel. 2. Left abdominal tumor: left abdominal tumors, such as lipoma, intestinal tumors, etc., when the tumor location is superficial, hard lumps can also be felt on the left side of the child’s belly button. 3. Inguinal hernia: due to the weak inguinal fascia and muscle, the tissues in the abdominal cavity will be protruded from the weak place of the left inguinal area, forming a hernia, which can be manifested as a hard lump on the left side under the belly button. Children with hard lumps on the left side of the navel, you should go to the hospital in a timely manner, improve the relevant examination, identify the cause of the disease to give targeted treatment.