The most likely cause of swollen and painful gums in children is apical periodontitis, which can be treated with anti-inflammatory drugs such as erythromycin granules to reduce inflammation, while the teeth should also be treated with root canal therapy of the milk teeth in order to resolve the pain and control the infection. Children’s swollen gums are mainly caused by pulpitis leading to periapical inflammation, the main symptom is the periapical area of the mucous membrane appears red, swollen, pressure and pain, or even long pus, the symptoms of severe facial swelling. In addition to anti-inflammatory drugs for anti-inflammatory treatment, the most important thing is to take children to the hospital for root canal treatment of milk teeth, remove the infected pulp nerve, rinse, disinfect the pulp cavity, remove the source of infection. Inflammation in the apical region of the tooth can be gradually metabolized and absorbed by the child’s body. Periodontitis of milk teeth must be treated in time, because there will be permanent tooth germs developing in the alveolar bone below the milk teeth, and if the inflammation of the periapical area is left untreated for a long period of time, it will lead to abnormal development of the permanent tooth germs.