Chemotherapy in Treating Children With Recurrent or Refractory Sarcomas

sarcoma, recurrent childhood rhabdomyosarcoma, recurrent osteosarcoma, embryonal childhood rhabdomyosarcoma, alveolar childhood rhabdomyosarcoma, recurrent childhood soft tissue sarcoma, extraosseous ewing sarcoma/peripheral primitive neuroectodermal tumor, recurrent ewing sarcoma/peripheral primitive neuroectodermal tumor, interventional, phase2