Objective To explore early warning indicators for extracorporeal membrane oxygenation (ECMO) in children with fulminant myocarditis (FM) and their association with prognosis. Methods Clinical data of 22 children with FM admitted to the Pediatric Intensive Care Unit of Hainan Women and Children's Medical Center from June 2019 to June 2025 were retrospectively analyzed. Patients were grouped by ECMO support (ECMO group, n=10; non-ECMO group, n=12) and by outcome (survival group, n=17; death group, n=5). Data on demographics, laboratory values, echocardiographic measurements, and treatments administered were collected. The predictive value of early warning indicators for initiating ECMO was assessed by receiver operating characteristic (ROC) curve analysis. Results Compared with the non-ECMO group, the ECMO group had lower left ventricular ejection fraction (LVEF) and fractional shortening (FS), and higher peak brain natriuretic peptide (BNP), peak vasoactive-inotropic score (VIS), peak lactate, and a higher proportion of interventricular septal and ventricular wall hypokinesis (all P<0.05). ROC analysis showed that peak BNP >21 650 pg/mL predicted the need for ECMO with a sensitivity of 80%, specificity of 82%, positive predictive value of 80%, negative predictive value of 60%, and an area under the curve of 0.771 (P<0.05). The overall mortality was 23% (5/22). Compared with survivors, non-survivors had lower Pediatric Critical Illness Score (PCIS), LVEF, and FS, and higher peak VIS, peak lactate, lactate level at 24 hours after treatment, and a higher rate of ECMO use (all P<0.05). Conclusions Peak BNP >21 650 pg/mL has early warning value for determining the need for ECMO support in children with FM. PCIS, LVEF, FS, VIS, and lactate are useful for assessing disease severity and prognosis. ECMO is a critical life-support modality for extremely severe FM.