Poor resistance and illness in children under five years of age is mainly related to age. First of all, immune system diseases, such as immunodeficiency diseases, need to be ruled out. Usually, it is necessary to start with prevention, mainly of respiratory tract infections as well as digestive tract infections. This includes strengthening children’s physical fitness, for example, by increasing and decreasing clothing according to the seasons and the weather. Clothing should not be too much or too tight, but should be increased or decreased with the temperature, so that the mucous membrane of the skin can be exposed to hot and cold air, exercise their own response to hot and cold, and go outdoors more often. Pay attention to children’s nutrition, ensure a balanced diet, prevent vitamin A, C, D, E and calcium, iron, zinc and other trace elements deficiencies, and enhance the body’s immune system. Prevent respiratory tract infections. During the season when respiratory tract diseases are at their peak, contact with patients with respiratory tract infections should be reduced, and go to places with a lot of people and dirty air as little as possible.