This study will seek to determine if rapid genomic sequencing improves outcomes for acutely ill infants. The investigator will enroll up to 1,000 acutely ill infants in a prospective, randomized, blinded study to either rapid Whole Genome Sequencing (WGS) or rapid Whole Exome Sequencing (WES, which is 2% of the genome and ~4-fold less expensive). Outcomes will be measured both by objective clinical measures and family perceptions (patient/family centered outcomes). Primary analysis of WGS or WES will be in infants alone. Secondary analysis, in infants who do not receive a diagnosis, will be of families - ideally trios (mother, father, and affected infant), which is ~2-fold more expensive. Trios will be analyzed within the same randomization arm (WGS or WES). This study is designed to quantify which acutely ill infants benefit from rapid genomic sequencing, by how much they benefit, how they benefit, which rapid genomic sequencing method is superior, and the cost effectiveness of such testing.