COG A Phase II Study of the Raf Kinase and Receptor Tyrosine Kinase Inhibitor Sorafenib (IND# 69896) in Children and Young Adults with Relapsed/Refractory Rhabdomyosarcoma; Wilms Tumor; Hepatocellular Carcinoma; and Papillary Thyroid Carcinoma Pediatric CIRB Completed Completed