The COVID-19 pandemic has impacted the epidemiology of other infectious diseases. In particular, the respiratory syncytial (RS) virus infects almost all children during their first or second year of life. However, during the COVID-19 pandemic, many restrictions were enforced that isolated children from other children. Therefore, we hypothesized that the clinical features of RS virus infection were altered and conducted a study to evaluate these changes. This observational study included children below the age of six years who were admitted to the Tokyo Metropolitan Toshima Hospital. Their clinicodemographic data were extracted from medical records. The 369 children eligible for the study were assigned to three groups: "pre-pandemic" (group 1, n = 253); "during pandemic" (group 2, n = 77), and "post-pandemic" (group 3, n = 39). Logistic regression analysis revealed that compared to group 1, the odds ratio (OR) for oxygen use was significantly higher in groups 2 (OR 1.85. 95% confidence interval [CI] 1.06-3.23; < 0.05) and 3 (OR 3.36, 95% CI 1.59-7.12; < 0.01), and the use of mechanical ventilation was significantly higher in group 3 (OR 4.89, 95% CI 1.71-13.94; < 0.01). This study highlights changes in the clinical features of RS virus infection during and after the COVID-19 pandemic.