The digestive function of children’s stomach and intestines can gradually approach that of adults at the age of about 3 years old in preschool, and they can eat the same meals as adults, before that, children’s gastrointestinal development is still immature and prone to problems. In infancy, the stomach is horizontal and the upper pancreatic sphincter is relaxed while the lower pylorus is tense, making it easy for milk to reflux from the stomach to the esophagus, causing overflow. The volume of the stomach during infancy is also relatively small, 30-35ml for a full-term newborn, increasing to 100ml at 3 months and reaching 300ml at 1 year. The younger the child is, the less gastric acid is secreted, the poorer the activity of pepsin, and the digestive ability is relatively weak, while the digestive function of the stomach gradually strengthens as the child gets older. The intestinal canal of infants and young children is relatively long, more than six times their own length, relatively poor prone to intussusception, intestinal torsion. Although the intestinal mucosa is well developed and rich in blood vessels and lymphatic vessels, the grassroots development is still relatively poor, the intestinal wall is thin, and the ability to resist diseases is not perfect, so infectious agents, toxins and allergens in the intestinal cavity can easily enter the bloodstream through the intestinal tube, thus causing systemic infectious diseases and allergic reactions.