While mortality in U.S. pediatric intensive care units (PICUs) is improving, surviving children frequently develop persistent physical, cognitive, and psychological impairments. Over half of critically ill children experience potentially preventable PICU-acquired morbidities, with mechanically ventilated children being at greatest risk. In critically ill adults, randomized trials have shown that progressive mobility, started early (within 3 days of initiating mechanical ventilation), decreases muscle weakness and the duration of mechanical ventilation. However, similar randomized studies have not been conducted in the PICU. The investigator's prior studies revealed that less than 10 percent of critically ill children at the highest risk of functional decline are evaluated by a physical or occupational therapist within 3 days of PICU admission. Given the interplay of sedation, delirium, sleep, and immobility in the PICU, single-component interventions, such as sedation protocolization, have not consistently shown benefit for decreasing mechanical ventilation duration. Thus, the investigators developed the first pediatric-specific, interprofessional intervention (PICU Up!) to integrate goal-directed sedation, delirium prevention, sleep promotion, and family engagement into daily PICU care in order to facilitate early and progressive mobility. The investigators have demonstrated the safety and feasibility of this pragmatic, multifaceted strategy in both single-site and multicenter pilot studies. Hence, the next phase of the investigators research is to evaluate the clinical effectiveness and delivery of the PICU Up! intervention across a range of PICU patients and health systems. The investigators propose a pragmatic, stepped-wedge, cluster randomized controlled trial that will include 10 academic and community hospitals in the United States, with the following Aims: 1) Evaluate if the PICU Up! intervention, delivered under real-world conditions, decreases mechanical ventilation duration, measured as days alive and ventilator-free (AVF) through Day 21 (primary outcome) and improves delirium and functional status compared to usual care in critically ill children; and 2) Conduct a multi-stakeholder, mixed-methods process evaluation to identify key contextual factors associated with delivery of PICU Up!. If proven effective, the PICU Up! intervention has potential to profoundly change medical care in the PICU and substantially impact public health by improving outcomes for the growing number of pediatric survivors of critical illness.