Interesting, but also sad and dark...

So...the grandmother gave Laura arsenic and called it "magic powder," but for what purpose? Then Laura unwittingly kills her mother and the step-daughter does the same to Laura...I would call it karma, if it weren't for the fact that they were innocent and ignorant children who had no idea what they were doing. I wonder why the author wrote such a story? Was it to point out how we, as a society and or as a world, unwittingly do terrible things to the detriment of other people?