Childhood Soft Tissue Sarcoma

This observational study is to better understand how children and their families recover after the stress of major surgery for cancer so that investigators can create ways to improve resilience during recovery. The main questions it aims to answer are: 1. Can information obtained from patients and their caregivers wearing smartwatches and answering questionnaires be used to measure how patients are recovering from surgery? 2. Are there specific patterns in patients' circulating proteins and metabolites that are associated with stress after surgery? Participants, including pediatric patients undergoing surgery for cancer and their primary caregiver, will be asked to: * wear a smartwatch * complete questionnaires * allow for extra blood to be drawn for this research study when they are having their regular blood draws for clinical purposes These actions will occur at baseline prior to patients' surgery and then afterwards for up to one year. There are no changes to participants' clinical care or surgical care as a result of the study. Investigators will also collect participants' clinical information and cancer-specific outcomes. Participants will be remunerated for their time.

RAD3CAR is a phase I study designed to evaluatethe safety of B7-H3-CAR T cells and lymphodepletion in combination with hypofractionated radiation therapy. Primary objective: \- To evaluate the safety of B7-H3-CAR T cell therapy after priming with hypofractionated radiation therapy (HFRT) and lymphodepleting chemotherapy in patients ≤ 21 years of age with relapsed/refractory B7-H3+ sarcomas. Secondary objectives: * To describe the antitumor activity of B7-H3-CAR T cells in combination with HFRT * To determine if B7-H3-CAR T cells traffic to tumor sites after combination treatment with HFRT