Sorafenib and Topotecan in Refractory/Recurrent Pediatric Malignancies

H. Lee Moffitt Cancer Center and Research Institute will be the Sunshine Project Coordinator, but will not be recruiting locally. The purpose of this research study is to establish a dose of the combination of drugs, Topotecan and Sorafenib in children. This will be called the maximum tolerated dose. The chemotherapy in this study is a combination of Topotecan and Sorafenib. The investigators are trying to find the highest dose of Topotecan and Sorafenib that can be given safely to children with Refractory or Recurrent Pediatric Solid Malignancies. The investigators will do this by testing different doses of these drugs in different groups of children. The investigators will also study how the body processes these drugs.