This overarching study aims to follow children across their entire healthcare trajectory to advance our understanding of children that present to the emergency department (ED) and/or are admitted to the hospital for severe acute SARS-CoV-2 infections, multisystem inflammatory syndrome (MIS-C), myocarditis, and pericarditis and detect signals of emerging syndromes in children. The specific aims of this study are; * To evaluate the short and long-term clinical outcomes and health consequences among children diagnosed with acute COVID-19 illness and their families, compared to SARS-CoV-2 negative controls and their families. * To evaluate the predictors (or risk factors) for severe disease and poor outcomes (hospitalization, critical illness, and mortality), from COVID-19 by comparing characteristics of children with/without COVID-19 who do and do not experience severe outcomes. * To compare the short- and long-term outcomes and health consequences among children with myocarditis, pericarditis and MIS-C occurring as a) adverse events following SARS-CoV-2 immunization (AEFIs) and b) as complications of SARS-CoV-2 infection and to assess consequences for their families. * To examine equity considerations in COVID-19 acute disease, events following vaccination, and long-term outcomes by applying social and structural determinants of health lens including but not limited to analyses based on race/ethnicity/Indigenous identity, immigration status, gender, LGBTQIA2S+ identity, language, disabilities, and household income level. * To collect biological samples from patients with confirmed MIS-C, myocarditis, and pericarditis following SARS-CoV-2 vaccination or infection and appropriate, matched controls for biobanking and later inclusion in national and international studies into the causes and risk factors of AEFIs and MIS-C (Translational sub-study). Additionally, samples will be collected from unmatched controls.