Level 1: Causes of Infant Diarrhea Infant diarrhea refers to an increase in the frequency of defecation in infants and young children, an increase in the amount of stool, a thin or watery texture, and is accompanied by symptoms such as abdominal distension, abdominal pain, and vomiting. The main cause is intestinal infection, including microbial infections such as bacteria, viruses, and parasites. In addition, overfeeding, improper diet, and underdevelopment of the digestive tract may also cause diarrhea in infants.