It is not necessary for the child to have had a frightening experience with any of the objects of their fears. It will certainly not help to coerce them to overcome their fear by forcing them to confront the objects of their fears. There is a good chance that dragging your screaming child towards a dog or throwing her into a swimming pool is going to backfire. Children most often outgrow these fears themselves. Sometimes they find that acting out the fear, like pulverizing a stuffed toy dog, is therapeutic.
Some children are scared of death and dying.
They cannot understand what happens to their pets or people who die. This is not surprising as adults themselves are confused by death. Adults themselves find it difficult to comprehend the finality of it all and its relation to life. Some parents choose to explain death in religious terms. They tell their child that the deceased has gone up to God in heaven.