There are very many causes of lymph node enlargement in children, such as infections, malignant tumors, benign diseases of the immune system, lipid deposition diseases, and endocrine system diseases. 1. Infectious diseases: including viral infections, bacterial infections, fungal infections, chlamydial infections, spirochete infections, parasitic infections, rickettsial infections. 2. Malignant tumors: such as malignant lymphoma, leukemia, malignant histiocytosis, amyloidosis and so on. Lymph node metastasis of malignant tumors: such as breast cancer, lung cancer, melanoma, head and neck cancer, gastrointestinal tumors, germ cell tumors and so on. 3. Benign diseases of immune system: autoimmune system diseases: such as rheumatoid arthritis, systemic lupus erythematosus, mixed connective tissue disease, dermatomyositis, dry syndrome, serum sickness, graft-versus-host disease, primary biliary cirrhosis and so on. 4. Lipid deposition diseases: e.g. Gosheimer’s disease, Niemann-Pick disease, etc. 5. Endocrine system diseases: hyperthyroidism, etc. 6. Other diseases: such as acute lymphadenitis, nodular disease, lymphomatoid granulomatosis, Langerhans histiocytosis, lymph node inflammatory pseudotumor, infectious mononucleosis, etc.. It is recommended to actively seek medical attention to clarify the cause of the disease and carry out targeted treatment.