As far as punishing parents, grandparents, any relative....or neighbors who have a child die in their pool.......that depends. Was there negligence? Egregious negligence? I ain't a lawyer but I totally expect that there are multitudes of negligence ---or criminal --case law that have addressed that very issue vis-a-vis drownings in backyard swimming pools.
But pools ain't guns. And guns ain't pools.
They are different.
Guns are inherently dangerous due to their lethality, portability, concealability, and ease-of-use. Everybody knows that. Except maybe young children. Accordingly, ownership of guns demands an extra level of care...by several factors.... than does ownership of say, kitchen knives or golf clubs, both of which have been used to kill.
And that is my point: Guns are markedly different. Far different than other elements, tools, substances in our human interactions with the world. Accordingly, gun ownership needs be imbued with a much much higher level of responsibility. And, liability when the fired gun harms innocents.