Seasonal outbreaks of respiratory syncytial virus are common among young children and represent an important clinical problem. The infection can affect all floors of the respiratory system. Respiratory syncytial virus is highly infectious and is the most common aetiological agent of bronchiolitis. It is estimated that 90% of children develop respiratory syncytial virus infection by the age of 2 years. In Poland and other countries of the northern hemisphere, these infections usually occur between October and May, with a peak in January–February. During the global COVID-19 pandemic, a significant change was observed in the epidemiology of respiratory syncytial virus infections in Europe and worldwide. The massive use of nonpharmacological interventions, such as closing nurseries, kindergartens, limited interpersonal contact, social distancing, strict hygiene rules and the use of protective masks, resulted in the absence or episodic occurrence of many seasonal infections, including those of respiratory syncytial virus aetiology, in 2020. In 2021, a so-called compensatory epidemic of syncytial virus aetiology was observed, i.e. a significant increase in the incidence associated with the extinction of collective immunity and an increasing proportion of susceptible individuals. The aim of the present study was to retrospectively analyse the incidence of respiratory syncytial virus infections in children hospitalised in the Department of Paediatrics, Paediatric Nephrology and Allergology of the Military Institute of Medicine in Warsaw in the years 2020–2021. We also discussed the prevention and treatment of infections, as well as the association of bronchiolitis with the development of asthma in children.