Lactase is an enzyme secreted by the body’s small intestine, located in the brush border of the small intestine mucosa, which can break down lactose into glucose and galactose. Lactose intolerance: When lactose in food enters the small intestine, lactose cannot be broken down into monosaccharides and absorbed into the blood due to lactose deficiency (LD ), which is called lactose malabsorption (LM). When lactose enters the colon, it is fermented by bacteria to produce short-chain organic acids and gases, and the fermentation process can cause bowel sounds, abdominal pain, bloating and osmotic diarrhea. The above process is called lactose intolerance (LI). Lactose: a disaccharide, a disaccharide present in mammalian milk; formed by the condensation of one molecule of glucose and one molecule of galactose, slightly sweet, containing about 4% of lactose in cow’s milk and 5-7% in human milk. Lactose is one of the main nutrients needed for children’s growth and development. In nature, only the milk of mammals contains lactose, and various plant foods do not contain lactose. Lactose is broken down into one molecule of glucose and one molecule of galactose by lactase and is absorbed and used by the body to supply us with calories. 2, promote brain and nervous system development: the development of brain cells and the soundness of the entire nervous system of children need a large amount of lactose, galactose is particularly important for children’s brain development, he can promote the production of cerebroside lipids and mucopolysaccharides. 3.Intestinal function: In the intestine, lactose generates lactic acid under the action of lactobacillus, lactic acid streptococcus, various enzymes and microorganisms, and lactic acid can inhibit the reproduction of harmful bacteria in the intestine, which has an adjusting and protective effect on pediatric gastrointestinal.