That mother is a fool! I would never let my child get into a position they could get hurt- its hard enough to keep them safe when you are vigilant in their behaviors. You have a good manager. Too bad you didnt have another employee near you that could have gotten the manager when this happened while you stayed to stop the child.
Unfortunately= even if you tried to stop the child, if the child did get hurt, they could actually sue.. You were right to intervene. In the post office, we had what was called a incident report. You just write what happened incase later they do try to sue the company. Ask your manager about it. Also the manager has the right to tell the people not to return to such a situation, and maybe the manager to see if they come back in.. YOu have the right to protect the companies " property" which the animals are part of that..