Well, I think the parents were clearly negligent. However, I think we need to be careful about rushing to judgments. A lot of people in here are making the assumptions that cancer care is cheap or that it is easy to diagnose. It's not. Even finding a good oncologist can be difficult if you are in a rural area.
I had Hodgkin's Lymphoma for possibly 6-8 months before I felt sick enough to go to the doctor. I received an Xray that revealed something was seriously wrong. It still took two biopsies and about 2.5 weeks before a diagnosis was made. During this time I also received a bone marrow biopsy and an outpatient surgery to remove fluid build up near my lungs. Then it was six months of chemo and radiation. The total cost of my treatment was probably around $1.5 million, though honestly I have no real idea. Free clinics aren't going to offer the type of services needed to treat cancer. They are for the flu

I highly doubt emergency room services will do the proper checks for cancer either, though in lymphoma's case an Xray will pick it up.
This reveals some of the major flaws in our health system, and we shouldn't brush them aside due to the rather sad nature of this particular case.
Cancer is a major problem for low income families simply because they often do not receive great routine care. Yes, Medicaid can help, but it can be very difficult finding a doctor who will take Medicaid. I discovered this myself after I finished treatment and went back to school. And the income limitations for Medicaid are incredibly stringent.
I think we need to be careful about rushing to judgements. If I recall correctly, a few years ago a religious family stopped bringing their child to chemo for Hodgkin's because they had religious objections. He got worse and eventually CPS intervened...ended up in court, created a big fuss.