BACKGROUND: SARS-CoV-2 can potentially cause nosocomial outbreaks. Although high secondary attack rates (SARs) among adult roommates have been reported, data on pediatric settings are limited. This study aimed to evaluate the SAR of symptomatic SARS-CoV-2 infections in shared rooms in a children's hospital. METHODS: A retrospective chart review from January 1, 2023, to December 31, 2023, was conducted at the National Center for Child Health and Development, one of the largest tertiary children's hospitals in Japan. According to hospital policy, nucleic acid amplification tests for SARS-CoV-2 were required for all hospitalized patients who developed new-onset fever or respiratory symptoms during the study period. If the test result was positive, confirmed cases with SARS-CoV-2 infection were immediately transferred to an isolation ward, and their remaining roommates were closely monitored for 5 days following the diagnosis of the index case. The SAR of symptomatic SARS-CoV-2 infections among roommates was calculated. RESULTS: Eighteen patients were identified as index cases with whom a total of 53 roommates had contact. Among these exposed roommates, secondary symptomatic SARS-CoV-2 infections occurred in 2 shared rooms, and the SAR within 5 days after the exposure from the index case was 5.7% (3/53). CONCLUSIONS: The SAR of symptomatic SARS-CoV-2 infections in the largest tertiary children's hospital in Japan was not high in this study. Further studies are warranted to validate our findings and to establish effective isolation and surveillance strategies for SARS-CoV-2 in hospitalized children.