Talotrexin in Treating Young Patients With Recurrent Solid Tumors or Leukemia That is Recurrent or Does Not Respond to Treatment

DISEASE CHARACTERISTICS: * Diagnosis of either of the following: * Recurrent solid tumor * Histologically confirmed\* malignancy at original diagnosis or relapse * Measurable or evaluable disease * Lymphoma or primary CNS tumor allowed * Patients with CNS tumors must be on a stable or decreasing dose of dexamethasone for the past 7 days * Recurrent or refractory leukemia * Confirmed relapse, as defined by M3 marrow (25% blasts in bone marrow aspirate or biopsy) * Active extramedullary disease allowed provided there is no leptomeningeal involvement NOTE: \*Histological confirmation not required for intrinsic brain stem tumors * Bone marrow metastases allowed * Not refractory to red blood cell or platelet transfusion * No pleural effusion or significant ascites * No known curative therapy or therapy proven to prolong survival with an acceptable quality of life exists * No Down syndrome PATIENT CHARACTERISTICS: * Karnofsky performance status (PS) 50-100% (for patients \> 10 years of age) OR Lansky PS 50-100% (for patients ≤ 10 years of age) * Absolute neutrophil count ≥ 1,000/mm³ (for patients with solid tumors without bone marrow involvement) * Platelet count ≥ 100,000/mm³ (transfusion independent) * Hemoglobin ≥ 8.0 g/dL * Creatinine clearance or radioisotope glomerular filtration rate ≥ 70 mL/min OR creatinine adjusted according to age as follows: * No greater than 0.6 mg/dL (1 year to 23 months) * No greater than 0.8 mg/dL (2 to 5…