There are three main causes of abdominal pain and vomiting in children: 1. Acute gastroenteritis, mainly due to children eating unclean food, causing intestinal spasm, producing symptoms of vomiting, nausea and diarrhea. 2. Acute appendicitis, mainly due to inflammation of the appendix caused by low immunity in children or blockage of fecal stones in the lumen of the appendix, manifesting as metastatic right lower abdominal pain, accompanied by nausea, vomiting and fever. 3. Mesenteric lymphadenitis, which mainly manifests as vague pain or paroxysmal colic in the abdomen and may be accompanied by symptoms of diarrhea and fever. The diagnosis of these three diseases can be made by medical history, physical examination of the abdomen, as well as ultrasound of the abdominal cavity and routine blood tests.