Childhood Alveolar Soft-part Sarcoma, Childhood Angiosarcoma, Childhood Epithelioid Sarcoma, Childhood Fibrosarcoma, Childhood Gliosarcoma, Childhood Leiomyosarcoma, Childhood Liposarcoma, Childhood Neurofibrosarcoma, Childhood Synovial Sarcoma, Previously Treated Childhood Rhabdomyosarcoma, Recurrent Childhood Rhabdomyosarcoma, Recurrent Childhood Soft Tissue Sarcoma, Recurrent Ewing Sarcoma/Peripheral Primitive Neuroectodermal Tumor, Recurrent Osteosarcoma