This trial is testing olaparib, a medication, to see if it is safe for children and teenagers with certain hard-to-treat tumors. These patients have tumors that have come back or haven't responded to other treatments. Olaparib works by stopping cancer cells from fixing themselves, which can help to kill them. Olaparib has been approved for use in various cancers, including ovarian and breast cancer, and has shown promising activity in both adult and pediatric patients.