BACKGROUND: Data on the presentation, management and outcomes of Lassa fever (LF) in children are limited. METHODS: Description of the clinical and biological features, treatment and outcomes of RT-PCR-confirmed LF in children aged under 15, enrolled in the LASCOPE prospective cohort study in Nigeria between April 2018 and February 2023. RESULTS: 124 children (aged under 12 months: 19; over 12 months: 105) were hospitalized with RT-PCR-confirmed LF. All received intravenous ribavirin. During follow-up, 99/124 (80%) had fever; 71/124 (57%) had digestive symptoms, vomiting (n = 56/122, 46%) and abdominal pain (n = 34/78 aged ≥ 5 years, 44%) more often than diarrhea (n = 19/124, 15%); 17/124 (14%) had hemorrhagic signs; 44/112 (39%) had a hematocrit lower than 25%, of whom 32/44 (73%) received transfusions; 44/88 (50%) developed hypotension; 18/112 (16.1%) developed KDIGO ≥ 2 acute kidney injury; 10/112 (8.9%) had KDIGO 3 acute kidney failure; 4/124 (3.2%) underwent renal replacement therapy. 7 children died, including 4 aged under 12 months (case fatality rate: under 12 months - 22%, 95% CI 7 - 48%; over 12 months - 2.9%, 95% CI 0.7 - 8.7%). In univariable analysis, age (p=0.003), impaired consciousness (p=0.026), and Lassa RT-PCR Ct value (p=0.006) were associated to Day 30 mortality. CONCLUSIONS: The fatality rate for children over 12 months hospitalized with LF was lower than that previously reported for adults. Hypotension and acute kidney injury were the most frequent organ dysfunctions. Bleeding was relatively infrequent. Anemia and the need for transfusion were common, the relative contribution of ribavirin-induced hemolysis being unknown.< Réduire