The causes of swollen abdominal lymph nodes in children, i.e. mesenteric lymphadenitis, include viral infection, bacterial infection, and other causes. 1. Viral infection: mesenteric lymphadenitis is often associated with respiratory and intestinal infections, such as viral infections, common viruses include adenovirus, coxsackievirus, EBV and so on. It manifests as mesenteric lymph node hyperplasia, congestion and edema. Clinical symptoms include fever, vomiting, abdominal pain, diarrhea or constipation. 2. Bacterial infection: such as Staphylococcus aureus, hemolytic streptococcus, Escherichia coli and so on trigger the disease. Bacterial infected lymph nodes show acute inflammatory reaction, necrosis, hemorrhage, and bacteria can be isolated from the lymph nodes. 3. Other causes: such as parasites, Mycoplasma pneumoniae infection, lymphoma can lead to the disease. Meanwhile, poor living environment, low immunity, and lack of vaccination are risk factors for this disease. Children with enlarged abdominal lymph nodes may also have other causes, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment under the guidance of the doctor.