Eligibility criteria
We included published and peer-reviewed studies, which were observational, cross-sectional, retrospective, case series, brief reports and letters to the editor that reported clinical features or illness severity among children (<21 y) with COVID-19. Other reviewed items were epidemiological data, pediatric age categories, management, outcomes, imaging and laboratory findings. Due to the limited data of COVID-19 in children outside China, we decided to include letters to the editor from other countries that met the inclusion and exclusion criteria to increase the variability population. Only English language studies were included. Duplicate publications, review articles, case reports, editorials and opinion articles were excluded. We also excluded articles that did not have enough information about children since its main target was the adult population.
Information sources and search strategy
We conducted a systematic search of studies published from February 18th, 2020 to June 8th, 2020 in PubMed and other databases (ScienceDirect, SpringerLink, Ovid and Google Scholar). We used the MeSH terms; (”COVID-19” [Supplementary Concept]) AND ”Child”[Mesh]. The search ended on June 8th, 2020. Two different searchers independently evaluated the search results (GCLG, VCJA). Disagreements were resolved by a third searcher (ADL).
Study selection and data selection
First, we appraised the screening strategy by title and abstract, then full texts were evaluated by inclusion criteria, and finally peer reviewed. For each study we obtained the following variables: author´s name, country, year of publication, total number of patients, sex distribution, pediatric age categories (divided according agreement between studies as follows: <1y, 1-5 y, 6-10 y and >10 y),  previous contact with a family member infected, mean incubation period, diagnosis by real-time polymerase chain reaction (RT-PCR) and serum antibodies levels (IgM, IgG), illness severity, clinical features, number of patients admitted into the pediatric intensive care unit (PICU), complications, image-laboratory findings and management. We included the analysis of the Pediatric Inflammatory Multisystem Syndrome Temporally Associated with SARS-Cov-2 (PIMS-TS) and their own variables like clinical findings, complications, severity and mortality.
Definition for illness severity, was based on the clinical classification of COVID-19 in children, proposed by Shen K et al. [6] and definition of PIMS-TS reviewed by The Royal College of Pediatrics and Child Health (RCPCH) [17,18]. Available inSupplementary Material .