What to do if I want to become a pediatric oncology nurse?

Good. First you go nursing school, after graduation work for some time in med-surg-ped nursing for some time , after acquiring sufficient paediatric nursing skills, work in ped oncology to become paediatric oncology good luck.
Get nursing license. Obtain a RN and / or BSN degree in college studying nursing. After obtaining degree and obtaining state licensure, seeking work in a children's hospital pediatric hematology/oncology unit would be the next step.