1. What is the reason why babies have foamy diarrhea? Foamy diarrhea in babies may be caused by a variety of reasons. First of all, the baby may be caused by food allergies or indigestion. Secondly, if a breastfeeding mother eats more spicy and greasy food, it will also cause gastrointestinal discomfort in the baby. In addition, bacterial infections and viral infections may also cause diarrhea in babies.