The common causes of tummy ache in three-year-old babies are viral gastroenteritis, indigestion, intussusception and so on. 1. viral gastroenteritis: if the baby has unclean diet and unhygienic living habits, it is easy to cause rotavirus, norovirus and other infections, inducing viral gastroenteritis, which in turn appears as tummy pain, diarrhea, and drainage-like stools. 2. Indigestion: If the baby overeats or eats too much greasy, high-fat food, it is easy to cause food accumulation, resulting in indigestion. Usually babies will feel full and uncomfortable soon after eating, and also have middle and upper abdominal pain, burning sensation in the abdomen and other symptoms. 3. intussusception: three-year-old baby in the process of growth and development, due to the gastrointestinal tract function is very imperfect, the intestinal reverse peristalsis, at this time can cause the small intestine into the large intestine or ileocecal part of the, and then appeared in paroxysms of abdominal pain, blood in the stool, vomiting and other manifestations. If the three-year-old baby stomach pain, it is recommended to go to the regular hospital in time, clear diagnosis and timely treatment.