It can be said that oral cavity is a manifestation of health. The existence of harmony and con-cord in the mouth as a window of health is conditioned by the intact state of oral epithelia, balance of oral flora, normal function of a saliva gland, as well as general health status. A disruption of this harmony and any of its stated aspects can provoke the incidence of oral symptoms and oral diseases, which can endanger everyday vital functions and habits due to its specificities, and thus cause a problem of which we have been unaware. Oral mucosal diseases in children represent a separate area. A child’s organism is affected more intensely in comparison to an adult one, as is the case for all types of infectious diseases, and recuperates from some infections more easily and quickly than an adult patient. The most frequent oral diseases at childhood age are as follows: modification of oral mucosa that appears in infants and babies, inflammatory diseases, tongue diseases in children, recurring ulcerations and injuries of oral mucosa. This paper aims to give an overview of oral infectious diseases of children, and to stress the importance of clinical examinations, with differential diagnosis of modifications, at the mucous membranes of the oral cavity. A greater emphasis was placed on population education, in order to report in time to their physicians. By examining the oral cavity, a diagnosis can be made, without unnecessary and burdensome tests. Timely inspection, professional diagnosis, accompanied with an adequate therapeutic treatment are the prerequisites of high-quality child health care. Cooperation between parents and medical staff is necessary, together with accepting advice from a professional, from a physician, as well as from a nurse.