We wanted our children to understand death as much as their limited years would allow. No particular reason but we didn't want the reality of death to hit hard should it suddenly happen. Perhaps a little blunt as we feel 'when you're dead, you're dead', no room for ambiguity.
We told them that everything with a heartbeat dies, some sooner than others but generally when they are old and just like with a car, parts wear out and that's the end for them. We asked the children how there would be room for all the babies being born around the world if the very old people didn't die? (I know, I know but we were at a different stage in life and am now seeing the other side of the coin! I still feel it's true, though).
The same granddaughter peered at me intently and announced 'you're quite old, you may die soon', which is fine by me - not the dying but that the child has processed and accepted death. Years ago early death was common but with modern medicine far less so; today's children are not as conversant with death.
My daughter was once very ill in hospital whilst on their American holiday. Her five-year-old breezed in and brightly said 'Mummy, if you die, can I have your new sunhat?', so children can be pragmatic, too!