Children are more aware of death than we realize. Death confronts them at an early age. A pet dies. A funeral procession drives by. Religious discussions may focus on death.
Killings are common daily on television.
Very young children may believe in magic. Magic means that all things are possible and believable. Stones can talk, princes turn into frogs, beautiful princesses sleep 100 years and are awakened by a kiss from a handsome prince. To preschoolers, death is reversible. If you go on a trip you come back.