Patients with solid tumors are stratified according to tumor histology (neuroblastoma vs Ewing's sarcoma [closed to accrual as of 5/19/03]/peripheral primative neuroectodermal tumor [PNET] vs osteosarcoma [closed to accrual as of 5/19/03] vs rhabdomyosarcoma vs non-Hodgkin's lymphoma vs other solid tumors). Patients with CNS tumors are stratified according to tumor histology (medulloblastoma/PNET vs ependymoma vs brainstem glioma vs other CNS tumors).