WM is very careful about the safety of children. When I watch my grandchildren I am usually about 10 feet behind them. I told them it is like herding stray cats. During a typical store tour about 10 people will ask them where their parents or grandparents are.
If a child is lost, the store is locked and the aisles are combed methodically. They have stopped actual cases of abuse doing this.
Obviously someone was lax about securing the mirror. They are liable.
When I go to Home Depot, I try and leave the kids at home. If I must go, I keep them glued to my side. Too much stuff that could fall and the forklifts. However, going to Walmart, I am not as protective. I don't let them out of my sight. I just don't walk through the door thinking that something could kill them inside the store.