Talabostat Combined With Temozolomide or Carboplatin in Treating Young Patients With Relapsed or Refractory Brain Tumors or Other Solid Tumors

DISEASE CHARACTERISTICS: * Histologically confirmed solid tumors, including, but not limited to, any of the following: * Rhabdomyosarcoma and other soft tissue sarcomas * Ewing's sarcoma family of tumors * Osteosarcoma * Neuroblastoma * Wilms' tumor * Hepatic tumors * Germ cell tumors * Primary brain tumors * In patients with brainstem or optic gliomas, requirement for histological confirmation can be waived if biopsy was not performed * Patients with brainstem gliomas that did not respond to therapy but that are without radiographic evidence of disease progression must have clinical evidence of progression * Patients with brain tumors must be on stable or tapering dose of corticosteroids for 7 days prior to study entry * Measurable or evaluable disease * Relapsed or failed to respond to frontline curative therapy, including any of the following: * Surgery * Radiotherapy * Chemotherapy * Combination of modalities * No other potentially curative treatment options available PATIENT CHARACTERISTICS: * ECOG performance status 0-2 * Absolute neutrophil count ≥ 1,500/mm\^3 * Hemoglobin ≥ 8 mg/dL * Platelet count ≥ 100,000/mm\^3 (platelet transfusion independent) * Bilirubin ≤ 1.5 times upper limit of normal (ULN) * SGPT ≤ 2.5 times ULN * Creatinine clearance ≥ 60 mL/min OR age-adjusted creatinine\* as follows: * No more than 0.8 mg/dL (for patients ≤ 5 years of age) * No more than 1.0 mg/dL (for patients 6 to 10 years of age) * No…