 - Bone marrow harvest without prior PBSC collection: Children will undergo primed bone marrow harvest comprising GM-CSF IV or SC for 5 days prior to harvest to increase cellularity and then marrow is harvested. Marrow and blood specimens are also obtained with the initial bone marrow evaluation and at the time of harvest if a cytogenetic abnormality was previously described. Other patients who are unable to undergo PBSC collection may proceed with a bone harvest at the discretion of the protocol chairperson. 