What is the difference between pediatric oncology and hematology?

Different focus. Pediatric oncologogists diagnose, treat and care for children with cancer or malignancies. Some overlap with hematology because they are blood cancers. Pediatric hematologists deal with many blood problems, some which are cancers (leukemia), some which are minor (iron deficiency anemias), some which are life-threatening (aplastic anemia), some which are inherited (sickle cell, hemophilia).
See below. Hematology is the study of blood disorders, things like clotting disorders, red blood cell disorders, bleeding disorders. Oncology is the study of cancer. These two overlap when dealing with leukemia (cancer of blood cells) and lymphomas.
Different patients. Oncology is the care of cancer patients. Hematology is the care of patients with blood disorders. Most pediatric hematologist-oncologists treat both groups of patients, as the board certification in pediatrics is for both hematology and oncology.

Related Questions

How much time is a fellowship that specializes in pediatric oncology/hematology?

Several years. The path to being certified in pediatric hematology/oncology after completing college is: medical school (4 years), pediatric residency (3 years), pediatric hematology/oncology fellowship (3 years). Some do additional years as a research fellow if interested in doing independent research in the field as well. Good luck! Read more...
3 years minimum. After completion of medical school, one normally completes a Pediatric residency (3 years) and then a pediatric hematology/oncology fellowship (3 years minimum). Additional time in fellowship training may occur, particularly if the individual desires a research career. Read more...