Have you had an inconsolable five year old who lost a close relative or even pet? I prefer to use analogies and explanations they can understand and accept to help them understand the reality. It's not the same as presuming they have no concept of death. That's a very long way from shutting them down with lies, avoiding the topic, or "protecting" them from it. It's trying to be age-appropriate. I make no claims to be a perfect parent however.
When they're a little older and have more capacity to understand a fuller, more accurate, discussion is possible.