Enrollment will be sought within the first 96 hours following admission to RCH or an RCH network ICU or within 96 hours of meeting criteria for the study if the infant was not previously eligible. Patients and their family members who consent to participate will have their blood drawn and will be randomized to receive either rapid WGS or rapid WES. The initial symptom-driven analysis will be conducted on the patient's sample only (singleton analysis). If a diagnosis is not found promptly (within 24 hours) via a singleton analysis, the family (or any combination of parents and/or other family members) will be analyzed using the same technology that the patient was randomized to receive. Pathogenic and likely pathogenic variants (as determined by ACMG guidelines) that relate in part or in whole to the patient's current phenotype will be clinically confirmed and reported into the patients' medical record. Although the intention of the study is to return symptom-driven results to the medical record, the clinical report for confirmation of symptom-driven findings may include negative findings of testing. In the event that our analysis incidentally finds a pathogenic variant for which a treatment or intervention exists to improve morbidity and/or mortality, families may choose not to receive this additional information.