BACKGROUND: Strategies to mitigate the impact of COVID-19 in special populations are complex and challenging. Few studies have addressed the impact of COVID-19 on pediatric patients with cancer in low- and middle-income countries. METHODS: Multicenter observational cohort study with prospective records and retrospective analyses starting in April 2020 in 21 pediatric oncology centers distributed throughout Brazil. PARTICIPANTS: Patients under 18 years of age who are infected by the SARS-CoV-2 virus (confirmed diagnosis through reverse transcriptase-polymerase chain reaction [RT-PCR]) while under treatment at pediatric oncology centers. The variables of interest included clinical symptoms, diagnostic and therapeutic measures. The repercussions of SARS-CoV-2 infection on cancer treatment and general prognosis were monitored. RESULTS: One hundred seventy-nine patients were included (median age 6 [4-13] years, 58% male). Of these, 55.9% had acute leukemia and 34.1% had solid tumors. The presence of SARS-CoV-2 was diagnosed by RT-PCR. Various laboratory markers were analyzed, but showed no correlation with outcome. Children with low or high BMI for age had lower overall survival (71.4% and 82.6%, respectively) than those with age-appropriate BMI (92.7%) (p = .007). The severity of presentation at diagnosis was significantly associated with outcome (p < .001). Overall mortality in the presence of infection was 12.3% (n = 22). CONCLUSION: In children with cancer and COVID-19, lower BMI was associated with worse prognosis. The mortality in this group of patients (12.3%) was significantly higher than that described in the pediatric population overall ( approximately 1%).