Gastroenteritis is an infection in the stomach that causes diarrhea and sometimes vomiting. It is common in babies and children. It is caused by a virus or bacteria in the intestinal tract (bowels). Bacteria or viruses get to the intestinal tract by putting dirty hands, toys or other objects near or into the mouth.
It is more serious in babies and young children than it is in adults because the diarrhea can cause dehydration. Diarrhea and vomiting can cause the loss of important fluids and minerals from the body (dehydration).