Dude that is rough, no wonder it still hits you from time to time. Those poor parents.

I know you are probably just repeating the terms you were given at the time, but I would classify that 'freak accident' of a kid finding a live hand grenade left behind by an arms collector selling his house instead as 'wreckless negligence'. The grenade did exactly what it was supposed to do, the responsible adult(s) failed enormously.

Aside - I'm absolutely not trying to chide you, I just don't know how else to get my point across that we pass along these stories sometimes without questioning the framing of the story (I catch myself doing it).