The purpose of this study is to determine if a drug called sorafenib can shrink LGA tumors (low-grade astrocytomas) in children and adults. Previous research has given us a better understanding of this type of tumor by studying the genetic "make-up" of LGAs. From this research, the investigators found that a drug called sorafenib may stop the growth of tumor cells by blocking some of the molecules needed for cell growth and by blocking blood flow to the tumor. This trial is studying how well sorafenib works in treating patients with LGAs, and how the effects relate to the specific genetic "make-up" of your particular tumor. This testing of your tumor's genetic make-up is optional and requires available tumor tissue for testing. In summary, the aims of this study are: To see if sorafenib can shrink LGAs; how well sorafenib is tolerated in patients with LGAs; and, how the effects of sorafenib relate to the genetic make-up of individual LGAs (Optional Study)