For some, the subject is as stated above. For others, the subject is faulty workmanship- be it a mirror or a tunnel panel. I suppose it depends on your point of view.
For me, I feel a tremendous amount of sorrow for this family's loss and wish it had never happened. Is Walmart is to blame for having a mirror that was either installed poorly or is so poorly constructed that a 3 year old could knock it down, or is the parent to blame for not keeping a tighter reign on the child and for not anticipating the worse case scenario when out shopping?
This article is inconclusive and perhaps purposely so. I expect any video of the incident and inspection of the mirror hardware will provide better evidence as to what actually happened.
Having worked in the commercial interiors industry for over 25 years I must agree that the store is responsible for providing a well designed safe environment for their clientele. However, having family members who have worked for Walmart, I must also acknowledge there is a high incidence of customers who literally let their children run wild through the store unsupervised.
It is a sad occurence, there is probably blame to be shared on all sides.