You do not know if the child was within sight of the mother or not. Isn't it possible that the mom looked at her child every 5 seconds or so, but didn't happen to be looking at the particular moment the mirror fell?
On the other hand, I guess it is possible that the child was on the other side of a clothing rack, out of sight, but still within 5 feet.
A 3 year old, while out shopping, should not be in a place where the parent cannot see him/her.
*sigh* Go back and read the article. She only HEARD a crash.
When in a store, the childs safety is the responsibility of that parent.