Can there be such a thing as a pediatric oncology nurse?

Absolutely. These nurses are trained specifically to give chemotherapy to kids. They are also good at accessing ports, which are the long-term IV access that most kids have. They also become quite close to the kids during their treatment course.
Yes if you work. Yes if you work in paediatric oncology department and devote to paediatric oncology , and get trained as a paediatric nurse with special skills in oncology.