1. Birth to <18 years of age; AND 2. Positive nucleic acid test for SARS-CoV-2 within the past 7 days; AND 3. Hospitalized, <72 hours post-admission; AND 4. One or more signs and/or symptoms of COVID-19 illness within the past 72 hours, as follows: 1. Cough; OR 2. Fever (oral temperature >100.4°F/38°C); OR 3. Chest pain; OR 4. Shortness of breath; OR 5. Myalgia; OR 6. Acute unexplained loss of smell or taste; OR 7. New/increased supplemental oxygen requirement; OR 8. Acute respiratory failure requiring non-invasive or invasive ventilation; OR 9. Encephalitis.

An individual who meets any of the following criteria will be excluded from participation in this study: 1. Receiving therapeutic anticoagulation for treatment of a thromboembolic event diagnosed within the past 12 weeks; OR 2. Clinical-relevant bleeding (see criteria under Primary Outcome, below) within the past 72 hours; OR 3. Platelet count <50,000/µL within the past 24 hours; OR 4. Prothrombin time (PT) ≥2 seconds above the upper limit of age-appropriate local reference range within the past 24 hours; OR 5. Activated partial thromboplastin time (aPTT) ≥4 seconds above the upper limit of age-appropriate local reference range within the past 24 hours; OR 6. Fibrinogen level <75 mg/dL; OR 7. Severe renal impairment, as defined by estimated glomerular filtration rate (eGFR) <31 mL/min/ 1.73 m2, as calculated by the Schwartz formula; OR 8. Parent or legally authorized representative unwilling to provide informed consent for patient participation.