This study is recruiting pediatric patients who have been diagnosed with rhabdomyosarcoma (RMS). RMS is a type of cancer that occurs in the soft tissues of the body. The goal of the study is to compare the effects, good and/or bad, of giving less chemotherapy drugs to people with very low risk-RMS to find out which is better. Patients will be separated into two groups based on their tumor type: Low Risk and Very Low Risk. Participants in the Low Risk group will receive Vincristine, Dactinomycin and Cyclophosphamide. Participants in the Low Risk group will receive Vincristine and Dactinomycin. All participants will be tested for genetic differences (called MYOD1 and TP53). If any participant is found to have these genetic differences, they will receive Vincristine, Dactinomycin and Cyclophosphamide. Common side effects of chemotherapy include nausea, vomiting, hair loss, and fatigue (tiredness). Participants will receive the medications through an IV in their arm. Study participation is expected to last up to one year.

This study is recruiting pediatric patients who have been diagnosed with osteosarcoma. Osteosarcoma is the most common primary bone malignancy of childhood and adolescence. The goal of the study is to determine the feasibility of adding cabozantinib to standard MAP (high dose methotrexate, doxorubicin, and cisplatin) chemotherapy in patients with newly diagnosed metastatic osteosarcoma with a resectable primary tumor and to compare the effects, good and/or bad, of cabozantinib in combination with MAP versus MAP alone on people with newly diagnosed OST to find out which is better. Common side effects of chemotherapy include nausea, vomiting, hair loss, and fatigue (tiredness). Participants will receive the medications through an IV in their arm and PO. Study participation is expected to last up to 16 months.