A few things: 1) I grew up in a family that owned an equipment rental store. I was working with the equipment for as long as I could remember. For better or worse, I was throwing branches into chippers, loading bulldozers on trailers, operating backhoes...all of it from the time I started school. Not unlike posting young kids on motorcycles and letting them ride around racetracks, everyone has a different view of what is acceptable based on their level of comfort with a certain activity. 2) Depending on the age, make and model of the chipper (admittedly I did not read the story) it may have any number of safety mechanisms. It may also have none at all. The old drum chippers would suck down a limb as fast as you put it in. The newer disc chippers have hydraulic feeding drums which make "getting caught" less dangerous. As others referenced though, the feed bars and mechanisms are often rigged to be convenient, and thus, less safe.
Godspeed to the little boy, and much needed strength for the father and rest of the family to get through this, not going to be easy. What a tragic way to go, so f'ing sad.....having a son about that age, it hits home a little.
This. Old chippers are scary, man eating beasts. Regardless of the age of the chipper I won't let my kids anywhere near a self feeding unit, those safeties aren't engineered to work with 40 pound teeny people and too many opportunities for things to go wrong.