mother, why is that man sleeping inside the coffin?

mother : because he already die..
daughter : why did he die?
mother : because he is old and sick..
daughter : when you are old, you will sick and die too?
mother : yes dear..
daughter : i don't like that.. i don't like people to die..

<<--- or you can say it another way -->>

mother : because he already die..
daughter: why did he die?
mother : everybody dies.. that is normal..
daughter : then you will die?
mother : yes dear..
daughter : i don't want you to die..
mother : oh love, its not going to be soon.
daughter : don't leave me mother.don't die.

<<-- or another way -->>

mother : because it is his time to leave the world..
daughter : where is he going? why did he has to go?
mother : he is not going anywhere, dying is not the end, its a part of life.
daughter : what happen to him then?
mother : after that, he will meet God.
daughter : oh.. alright, i pray he will rest in peace..he must be happy to meet God..

kids are simple.. so, be simple to them..tell no lie but truth..

surah al-qiyamah (75:19-23) .

(19) Not [as you think, that you (mankind) will not be resurrected and recompensed for your deeds], but you (men) love the present life of this world, (20) And neglect the Hereafter. (21) Some faces that Day shall be Nâdirah (shining and radiant). (22) Looking at their Lord (Allâh); (23) And some faces, that Day, will be Bâsirah (dark, gloomy, frowning, and sad)