Viruses are a common cause of respiratory infections in children. This study sought to compare the performance of a rapid antigen test versus the polymerase chain reaction (PCR) method for detecting three viruses (respiratory syncytial virus [RSV], adenovirus [ADV], and influenza A/B ([INF A/B]). We herein report the results of a prospective study conducted as part of the Sciensano (Institute of Public Health in Belgium) acute respiratory infection (ARI) surveillance. Between October 2018 and April 2019, 140 nasopharyngeal cell samples were collected from 135 children hospitalized for ARI at the University Hospital Dinant Godinne (Belgium). The rapid antigen test came back positive for 71/140 (50.7%) samples, while PCR came back positive for at least one virus for 123/140 (87.8%) samples. We determined the sensitivity (Se), specificity (Sp), positive predictive value (PPV), and negative predictive value (NPV) of the rapid test compared to the RT-qPCR (PCR), which is used as the gold standard. The results for the rapid antigen test were as follows: Se 80.3%, Sp 100%, PPV 100%, and NPV 85% for RSV; Se 6.25%, Sp 99%, PPV 66.7%, and NPV 78.1% for ADV; Se 87.5%, Sp 98.4%, PPV 87.5%, and NPV 98.4% for INF.