Recurrent respiratory tract infections (RRTIs) are very common in children and a major challenge for pediatricians. They affect the children's quality of life, cause absences from school and lost parental working days, and repeated medical examinations, hospital admissions as well as antibiotic therapies lead to high costs for society. Given their prevalence and clinical importance, various prevention strategies have been developed. One of the most widely used is the administration of immunostimulants: i.e. molecules of bacterial or synthetic origin that interact with immunological mechanisms in vitro and in vivo. A number of studies have investigated their effects on cellular and innate immunity, and their clinical efficacy, but there is no consensus as to their real usefulness. The main aim of this review is to analyse the available data concerning the activity and efficacy of immunostimulants in preventing pediatric RRTIs. The majority of studies have shown that the number of infections decreases after immunostimulant treatment, but they are affected by various methodological weaknesses. Further studies are urgently needed to confirm whether, when and which immunostimulants should be used.