Pediatric patients are vulnerable to adverse drug reactions (ADRs), necessitating prompt monitoring of treatment-related adverse events (AEs). This study analyzed ADRs in pediatric COVID-19 patients using a modified trigger tool to identify AEs, followed by causality analysis with the Naranjo Algorithm, and evaluated the tool’s performance. A cross-sectional, single-center retrospective study was conducted at a hospital in Indonesia from August 2020 to July 2021, using total sampling of pediatric patients aged one to≥24 hours with COVID-19. AEs were identified using 23 triggers (15 laboratory result, eight drug-administration). A total of 242 positive triggers were detected among 120 patients (mean two triggers/patient, range one to four), corresponding to 527 suspected drug–event associations assessed for causality. The Naranjo Algorithm classified 357 (67.7%) associations as possible, 32 (6.1%) as probable, and 138 (26.2%) as doubtful. Accordingly, 389 ADR events were identified from the possible and probable categories. The most common ADRs from drug-administration triggers were peptic ulcers (84.2%), hypersensitivity (29.2%), and nausea (27.5%); from laboratory result triggers, increased aspartate aminotransferase (5.8%) and alanine transaminase (1.7%) were most frequent. These ADRs were most frequently associated with ceftriaxone (48.6%) and azithromycin (26.0%). Of the 12 trigger types detected, 11 identified at least one ADR, with PPVs ranging from 44.4% to 100%. The modified trigger tool showed potential utility in detecting ADRs in pediatric patients; prospective studies in routine practice are needed to strengthen pharmacovigilance.