At what age can you explain death to a child without freaking them out?

[Fibutton]

When my elder two were small, we had lots of pets, and when they died it was an insight as to how life isn't permanent, we buried them and explained that (in our opinion), all their thoughts and feelings had gone into the sky to baby Jesus..., and all that was left was the casing that held all those thoughts and feelings that we had to bury, this transcended to humans when my Grandmother died, and i was able to say the same thing to both of them, which they took in their stride quite well. Hope this helps x