1. What is infant diarrhea? Infant diarrhea refers to an increase in the frequency of defecation in a short period of time in infants and young children, and the stool becomes watery or yellow-green, and even has foam and a fishy smell. The main reasons are intestinal infection, indigestion, allergies, etc. 2. In addition to the above-mentioned increased frequency of defecation, watery stools and peculiar smell, the symptoms of infant diarrhea can also include abdominal distension.