Such great advice already on this thread. Taking care of yourself if highly important. On my unit we have lost 3 kiddos within the last 3 months all from different cancers and they all sting the same. Dealing with loss is always difficult but with children, personally, its s different kind of difficult because of the innocence and the time that they are robbed of.
As far as everyone asking you why you chose that field, be honest and quite frankly their opinion doesn't matter. Working on peds heme/onc is 90% of the time the most fun you will ever have at work. I laugh more at this job than I have at any other unit I've been on. Theres a lovely article written about peds heme/onc by a nurse called "the happy floor". Look it up and read it. So accurate.
Treat them like kids, play with them, empathize with their parents, and have fun and learn a lot. You will bond with their parents and the kiddos themselves and thats okay. They spend so much time with you during some of the most vulnerable moments of their life so you become important to each other.
Enjoy! Its equally rewarding and heartbreaking but it will be the biggest blessing of your life!