3-year-old children can be checked for Helicobacter pylori, which can be detected by breath test, gastric mucosal biopsy, fecal Helicobacter pylori antigen test, etc. The test is suitable for 3-year-old children, which can be detected by carbon 13 or carbon 14 breath test. 1. Breath test includes carbon 13 or carbon 14 breath test, which has the advantages of convenience, rapidity and high accuracy, and is more suitable for 3-year-old children. 2. Gastric mucosal biopsy is an invasive test that uses endoscopy, sampling forceps and other equipment to extract biopsy tissue from the lesion and send it to the pathology laboratory for observation and testing, in order to detect whether there are signs of H. pylori infection. This test is the most direct and objective, but is invasive. 3. Fecal H. pylori antigen test is a non-invasive test that takes a stool sample and performs a pathology test to check for the presence of H. pylori infection. If a child is at risk of being infected by H. pylori, it is important that he or she go to the hospital in a timely manner and do not take medication on his or her own, as this may cause unnecessary damage.