Background: Survival among children with high-risk solid tumors remains poor. Reprogrammed metabolism promotes tumor growth and may contain therapeutic liabilities. Tumor metabolism has been assessed in adults using intra-operative 13 C-glucose infusions. Pediatric tumors differ from adult cancers in their low mutational burden and derivation from embryonic tissues. Here, we used 13 C infusions to examine tumor metabolism in children, comparing phenotypes among tumor types and between childhood and adult cancers. Methods: Patients recruited to the clinical trial NCT03686566 received an intra-operative infusion of [U-13 C]glucose during tumor resection to evaluate central carbon pathways in the tumor, with concurrent metabolomics to provide a broad overview of metabolism. Differential characteristics were determined using multiple comparison tests and mixedeffect analyses. Findings: We studied 23 tumors from 22 patients. All of the tumors analyzed by [U-13 C]glucose contained labeling in glycolytic and tricarboxylic acid (TCA) cycle intermediates. Labeling in the TCA cycle indicated the activity of pyruvate dehydrogenase (PDH) and pyruvate carboxylase (PC), with PDH predominating. Neuroblastomas had high lactate labeling relative to other childhood cancers and lung cancer and were distinguished by abundant tyrosine catabolites consistent with catecholamine synthesis. Conclusions: Intra-operative [U 13 C]glucose infusions are safe and informative in pediatric cancer. Tumors of various histologies use glycolysis and oxidative metabolism, with subtype-selective differences evident from this small cohort. Expanding this cohort may uncover predictive biomarkers and therapeutic targets from tumor metabolism.