AT reports grants from Asociacion Española de Pediatra, Instituto de Salud Carlos III, Fundación para la Investigación Hospital 12 de Octubre, and Fundación para la Investigación Infanta SofÍa. All other authors declare no competing interests. AT and MJM are members of the EPICO-AEP Working Group and part of the Translational Research Network in Paediatric Infectious Diseases (RITIP). AG-S contributes to the registry of children with SARS-CoV-2 infection admitted to Pediatric Intensive Care Units of the SECIP. We thank the parents and caregivers of deceased children who provided consent for recording their children's data in the clinical registries. We thank all paediatricians and researchers who contributed to this letter and to the registries, especially Rafael González-Cortés (Pediatric Intensive Care Unit, Hospital Universitario Gregorio Marañón, Madrid, Spain; registry of children with SARS-CoV-2 infection admitted to Pediatric Intensive Care Units of the SECIP); Cinta Moraleda (EPICO-AEP; Fundación de Investigación Biomédica Hospital 12 de Octubre. Instituto de Investigación 12 de Octubre [imas12], Madrid, Spain; RITIP; and Paediatric Infectious Diseases Unit, Department of Paediatrics, Hospital Universitario 12 de Octubre, Paediatric Research and Clinical Trials Unit [UPIC], Madrid, Spain); Cristina Calvo (Paediatrics, Infectious and Tropical Diseases Department, Hospital Universitario La Paz, Instituto de Investigación Hospital La Paz [IDIPaz], Madrid, Spain; RITIP); Fernando Simón, María José Sierra, and Pilar Aparicio (General Directorate of Public Health, Ministry of Health and Social Welfare, Madrid, Spain); and Pablo Velasco (Department of Hemato-oncology, Hospital Infantil Vall D'Hebron, Barcelona, Spain; Hemato-oncology Registry for COVID-19 of the Sociedad Española de Hematologia y Oncologia Pediátrica). We also thank all the members of the EPICO-AEP and the registry of children with SARS-CoV-2 infection admitted to Pediatric Intensive Care Units of the SECIP.