I used to work at a pediatric hospice. Like others have said, it's a pretty small population. We were a new company and building a business revolving around kids dying is really hard. Most of the kiddos we got were babies with heart defects (amount other things) or teenagers with cp or the like whose lungs were crapping out and family didn't want a trach, ect. Oncology patients made up only a small part of our population as there were several big children's onc programs around and thry held onto their kids.
As far as how to get involved, volunteer at camps for kids with life limiting illnesses. You can do a sort of reverse networking find out where they are treated, who/where the docs are, ect.