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

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.
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.