What is a mature and harmfulness way of explaining death to a child?

I'm guessing "harmfulness" was supposed to be "harmless"?

Let's assume so.

As someone who was educated on the matter first hand at a very young age, I think the best thing is to be as up-front as possible as you can. Avoid using figurative language such as "kick the bucket" and other idiomatic expressions, as that sends the message that death is something to be feared (fearing death is sort of nonsensical, as it is the one inevitability in all our lives).

Ultimately, nothing TRULY prepares you for the myriad sensations of loss, but you can give the child an emotional advantage by allowing him time to come to terms with the impending death of loved ones over time.

Involve your kid in reflecting on life, too. This is paramount. It may sound macabre, but a really useful and fun exercise for the child to engage in is to have him construct out of paper his own tombstone, representative of him, complete with epitaph. Encourage him to make it personal and representative of himself. Join in with him. This helps in the reflection of the life he's living, and reminds him subtly of the fleeting nature of life.

Good luck.

Be honest and use short sentences. After 15 seconds ask if they have any questions, then drop it till they bring it up. Avoid the tendency to lecture.

I like the Full House episode when Michelle Tanner's goldfish died. Her dad said he was asleep for a very very very long time and was probably not going to wake up ever.

Being upfront and honest about it. Everyone will die. It's just a path that all living things take.

Just tell them everyone goes and they're in a happy and VERY PINK place.

what the hell is harmfulness?