Honesty is definitely the best policy when explaining death to a child or else they may develop fears and misconceptions.
However, you need not delve deep in the topic as the child may not understand all your points. Moreover, it can scare young children.
Thus, the trick is to explain as much as the child can handle. This often depends on the child’s age, personality, life experiences, etc. In addition, it is recommended to encourage an atmosphere of comfort and openness.