Puleeze you have no way of knowing who's fault this is, the kid might have not been touching a mirror which was improperly set up, he may have been climbing a secure mirror and broke it, or this could be a freak accident! Stop blaming the parent when you're clueless as to what happened..
No matter what the truth of the incident really is, one FACT is that she took her eyes off of her child in Wal-Mart..geez! Anything could happen in a second.