I would hope that no one here is actually bashing the children. They're children! They probably don't know better.
The issue here is putting the supervision of children under your charge paramount, over all other considerations. The very nature of children (that they often don't know better, for example) means that parenting them is difficult. I know we've all read horror stories of terrible "accidents" that have befallen children, at least in part attributable to inadequate supervision in situ. One of those terrors could have happened in the same exact context, under the same circumstances, as the incident detailed in the OP. For example, in pulling the pickle out of the jar, the child could have fallen, bringing the whole jar down on top of their own head. I shudder just to think about what the lack of supervision could have resulted in. It was lucky that in this case the only harm was material. That's the real focus here. Yes, we all are harmed (materially), in a way, from incidents like this, caused by inadequate supervision of children. But the real concern this highlights is the potential for physical harm to the chidren themselves or to others from actions children take while inadequately supervised.
And as I said before, there is no good answer. You can't point your finger and say that this person or the other is wrong and should do things differently, without risking putting forward a perspective that is distinctly incompassionate or unreasonable. It is a bad situation. It sucks. It causes bad things to happen.