This structured exercise program will incorporate a specially designed, low intensity, resistance based exercise regime created by our physical therapist. In addition to standard of care, it consists of strengthening, endurance, stretching and relaxation exercises tailored according to age and their ability to perform activities throughout their hospitalization. This exercise program will be done three times a week for 30-45 mins supervised by the same physiotherapist throughout hospitalization and will be self-administered every weekend. A home exercise program printout with the appropriate resistance exercises will be provided to the family upon discharge, with instructions on how often to complete throughout the week. Discharged children will attend one supervised exercise session per week with the physiotherapist for six weeks. The family and patient will also be provided a weekly sheet to check off the days they completed strengthening and endurance exercises.

The second arm of the study involves patients following standard of care during the HSCT period in the hospital with PT evaluation and management prescribed as needed by their transplant medical team including any additional PT interventions as a result of clinical indications. No additional intervention is incorporated in this group

Age 4-6 years: Target lower extremity, core and upper extremity strengthening and activity tolerance. With supervision by the PT, the patient will walk in their room, and complete the following through play: squat, single leg stance, climb onto couch, half kneel to stand, quadruped and tall kneeling.

Age 7-21 years: First component will be strengthening exercises completed in bed or on a mat while sitting or standing. Multiple levels of exercises will be available, so that the program can be tailored to each patient and to their ability to perform activities. The exercises included will focus on core, hip musculature, and upper extremity strengthening; including exercises in quadruped and prone positioning, as well as supine, sitting and standing. Thera-Band will be used to increase resistance as needed. The second component will be endurance. Since the patients will be confined to their room this will include ambulation within the room, recumbent or pedal exerciser and step ups.

Test of Endurance (Pre-transplant, at discharge, and 6 weeks discharge.)

Muscle strength

Change from Baseline Functionality at 6 weeks post discharge.

Change from Quality of Life measurements based off of physical, mental, and social categories at 6 weeks post discharge

Log of average time out of bed for each patient.