1. Why does a 7-month-old baby have diarrhea? 1.1 Dietary problems: 7-month-old babies are in the stage of adding complementary foods. If the food is inappropriate or has indigestion, it can easily cause gastrointestinal problems. 1.2 Babies who are 7 months old and infected with viruses have immature immune systems and are prone to contracting viruses and causing diarrhea. 1.3 Low resistance: If the body resistance of a 7-month-old baby is low, it is easy to be infected by bacteria and viruses, causing gastrointestinal problems. 2. How to prevent diarrhea in 7-month-old babies? 2.1 Eat a reasonable diet. When adding complementary foods to a 7-month-old baby, pay attention to the diet.