As someone who is close to a childhood cancer survivor, I have myself toyed with the idea of pursuing peds/onc, and I asked a former peds oncologist what advice they would give someone considering a career in this field. This is what they said (they asked to remain anonymous):
Pediatric Oncology is a hard career. It's hard to live with all the
sadness, fear, suffering, and tragedy that are the children's and families' daily life. But it is also one of the most satisfying subspecialties: very often your patients are cured; most patients can be helped to live longer and less painful lives and their families can be helped to adjust to their new reality; and when a child must die it is an honor to give them and their family the blessing of a graceful, hopefully dignified death.
It's not for everyone. The pay is lower than other specialties requiring the same amount of training and dedication. The hours are difficult. I often cried at the sadness and unfairness of these terrible diseases. But it was the most satisfying work I have ever done. I was able to really make a difference in the lives of my patients and their families.
I suggest that any medical student thinking of this career obtain and watch the series of videotapes about Childhood Cancer that Fred Rodgers (yes, Mr. Rodgers, he was a serious professional) made for the American Cancer Society. If they touch you inside, then this may be the career for you.
By the way, the American Society of Pediatric Hematology/Oncology has resources for medical students and residents.