Background <p>Acute gastroenteritis (AGE) remains one of the leading causes of morbidity in children worldwide, with viral pathogens constituting the predominant etiological agents. The implementation of non-pharmaceutical interventions (NPIs) during the coronavirus disease 2019 (COVID-19) pandemic substantially altered the transmission dynamics of infectious diseases, including enteric pathogens.</p> Objective <p>To evaluate the frequency and etiological distribution of pathogens causing pediatric AGE and to assess temporal changes before, during, and after the COVID-19 pandemic.</p> Methods <p>In this retrospective single-center study, 5,966 pediatric patients presenting with suspected AGE between June 2015 and June 2023 were included. Stool samples were analyzed for viral, bacterial, and parasitic pathogens using rapid antigen tests, toxin assays, and conventional culture methods. Patients were categorized into three epidemiological periods: pre-pandemic (June 2015–February 2020), pandemic (March 2020–June 2022), and post-pandemic (July 2022–June 2023). Statistical analyses were performed using appropriate tests according to variable distribution. Categorical variables were compared using the Pearson chi-square test, whereas continuous variables were analyzed using one-way ANOVA or the Kruskal–Wallis test, as appropriate. A two-sided p-value &lt; 0.05 was considered statistically significant.</p> Results <p>An etiological agent was identified in 2,214 of 5,966 patients (37.1%). Age and sex distributions were comparable across study periods (<i>p</i> &gt; 0.05). Overall pathogen positivity decreased significantly over time, from 40.4% in the pre-pandemic period to 36.3% during the pandemic and 30.3% in the post-pandemic period (<i>p</i> &lt; 0.001). Viral pathogens remained the predominant etiological agents throughout the study period. Norovirus was the most frequently detected pathogen, identified in 1,252 patients (21.0%), followed by rotavirus (7.9%) and adenovirus (4.5%). Among bacterial pathogens, <i>Salmonella</i> spp. was detected in 198 patients (3.3%), whereas parasitic and toxin-related pathogens were uncommon. Norovirus detection declined significantly over time, whereas rotavirus detection increased significantly during the post-pandemic period (<i>p</i> &lt; 0.001).</p> Conclusions <p>Viral pathogens remained the predominant cause of pediatric AGE throughout the study period. The implementation of NPIs during the COVID-19 pandemic was associated with a significant reduction in overall pathogen positivity and marked changes in pathogen distribution, particularly a decline in norovirus and a post-pandemic resurgence of rotavirus. These findings underscore the importance of continuous epidemiological surveillance to guide prevention strategies and optimize public health interventions.</p>