In this study, we want to find out more about the side effects of an investigational drug for relapsed or refractory atypical teratoid rhabdoid tumor and high-grade glioma, Gallium Maltolate (GaM) and what doses of GaM are safe for people to take. Everyone in this study will receive GaM which is still experimental and is not approved by the U.S. Food and Drug Administration. We do not know all the ways that this drug may affect people. We hope the information from this study will help us develop a better treatment for relapsed or refractory atypical teratoid rhabdoid tumor and high-grade glioma in the future.