Patients must have received their last dose of known myelosuppressive anticancer chemotherapy at least three weeks prior to study registration or at least six weeks if nitrosourea Myelosuppressive chemotherapy:* Subjects must have received their last dose of known myelosuppressive anticancer chemotherapy at least three (3) weeks prior to study registration or at least six (6) weeks if nitrosourea At least 21 days after the last dose of myelosuppressive chemotherapy (42 days if prior nitrosourea) Chemotherapy: patients must have received their last dose of known myelosuppressive anticancer chemotherapy at least three (3) weeks prior to study enrollment in the study or at least six (6) weeks for those receiving nitrosourea Patients must have received their last dose of known myelosuppressive anticancer therapy at least three (3) weeks prior to study enrollment or at least six (6) weeks if prior nitrosourea INCLUSION CRITERIA FOR STRATUM C: Patients must have received their last dose of known myelosuppressive anticancer therapy at least three (3) weeks prior to study enrollment or at least six (6) weeks if prior nitrosourea Myelosuppressive chemotherapy: must not have received myelosuppressive chemotherapy within 3 weeks of entry onto this study (excluding hydroxyurea)* Cytoreduction with hydroxyurea can be initiated and continued for up to 24 hours prior to the start of CPX-351 RECURRENT/ PROGRESSIVE DIPG (STRATUM 1): Patients must have received their last dose of known myelosuppressive anticancer therapy or immunotherapy at least 21 days prior to enrollment (42 days if prior nitrosourea) Patient must have received last dose of known myelosuppressive chemotherapy > 21 days prior to enrollment; > 42 days if nitrosurea Myelosuppressive chemotherapy: must not have received within 2 weeks of entry onto this study Patients with solid tumors must not have received myelosuppressive chemotherapy within 3 weeks of enrollment onto this study (6 weeks if prior nitrosourea) Cytotoxic chemotherapy or other anti-cancer agents known to be myelosuppressive; the duration of this interval must be discussed with the study chair and the study-assigned research coordinator prior to enrollment* >= 21 days after the last dose of cytotoxic or myelosuppressive chemotherapy (42 days if prior nitrosourea)