Clinical Study on the Effect of Probiotic Compound Powder on the Immunity Improvement of Preschool Children

Inclusion Criteria: * Preschool children, male or female, 5 to 6 years old; * Those with weak constitution and easy to get sick: One of them can be satisfied: AGet cold ≥ 3 times a year B Bronchitis or pneumonia ≥2 times per year C Rotavirus diarrhea ≥1 time per year * During the trial, participants agree not to take any drugs, supplements, or other dairy products containing probiotics; * During the trial, participants agree not to take any other prebiotic/bacterial drugs, supplements, or dairy products including yogurt drinks; * Willing to refrain from participating in other interventional clinical studies during the trial period; * Be able to fully understand the nature, purpose, benefits and possible risks and side effects of the research; * Willing to obey all test requirements and procedures; * Informed consent signed by parents or legal guardians. Exclusion Criteria: * Subject who is in the treatment of gastrointestinal diseases; * Subject who has lactose intolerance; * The subjects are currently suffering from other organic diseases that affect intestinal function, such as history of gastrointestinal resection, colonic or rectal cancer, inflammatory bowel disease, diabetes, hyperthyroidism or hypothyroidism, Hirschsprung's disease, scleroderma, anorexia nervosa, etc.; * Subjects have any of the following medical histories or clinically diagnosed diseases that may affect the evaluation of the test effect: obvious gastrointestinal dysfunction, liver, kidney, endocr…