A typical child knows about one child with cancer. Back-of-the-envelope, the number a child knows would be (incidence rate of childhood cancer) * (typical K-8 size), but doubled since they observe all grades ahead and behind them. Incidence rate is about 20 per 100,000 and we might assume a typical K-8 is about 2000 students, so (20 / 100000 * 2000 * 2) ~ 1.

The first figure shows an order of magnitude decrease in mortality over the last few decades from childhood cancer. The average child growing up in the 70s would know a child that died from cancer, and today they would not!