The article is devoted to the study of probiotics, their principle of action and clinical application. Particular attention is paid to the mechanisms of action of probiotics, including competition with pathogens in nutrient substrates and adhesion sites, synthesis of antimicrobial metabolites (bacteriocins, organic acids), intestinal barrier and modulation of the immune response. Additional considerations of the risks of using probiotics, including the possibility of developing systemic diseases, metabolic abilities and hyperstimulation of the immune system. The need for strict control of the safety of strains, including their identification, study of functional activity and confirmation of effectiveness in randomized economic studies is emphasized. Particular attention is paid to the benefits of multi-strain probiotics, which exhibit a synergistic effect due to different strains that increase therapeutic efficacy. In providing research data confirming their benefits in the fight against intestinal infections, antibiotic-associated diarrhea, respiratory diseases and other conditions. 14 species of live probiotic bacteria in high concentrations: L. casei, L. plantarum, L. rhamnosus, B. bifidum, B. breve, B. longum, L. acidophilus, L. lactis, St. thermophilus, B. infantis, L. bulgaricus, L. helveticus, L. salivarius, L. fermentum in the studies confirmed the ability to significantly increase the effectiveness of standard treatment for diarrhea regardless of etiology, reducing the risk of prolonged diarrhea. Eight studies demonstrated that multi-strain probiotics enhanced immune defense and protective properties of the mucous membranes in both infectious diarrhea and respiratory diseases. The results of the conducted analysis indicate the importance of using multi-strain probiotics for the prevention and treatment of infectious diseases in children, but it is necessary to monitor the need for research to clarify their long-term effects and safety.