I once bothered my parents by crying by saying similar things. In my case, “According to Nostradamus's great prophecy, the world seems to end in 1999. What will end is a nuclear war. There will definitely be a world war before that. Then I was a young man around that time, so I should go to war. If you go to war, you're bound to die. I'm afraid to die!” Like, when I think about it now and think about it carefully, I was crying because of a very strange logic. Well, overall, “I don't want to die! I don't want to die!” I wonder if they were saying that...
I wonder what my mother said. I wonder if they said something like “everyone is going to die, so it's fine.” Or did you say, “No one can avoid it”? I don't really remember, but I feel like they probably made me cry even more by saying that fact. However, I think it was very good now that I was able to seriously touch something like the truth that “everyone will die eventually,” which may just be the only truth in this world.
I cried “huh huh,” cried, cried, and fell asleep from crying. (It looks like Kawashima Eigo.) I woke up refreshed, or rather, in the morning I was worried about something else, and the death problem went awry. After doing that a few times, I think I learned to put it on hold. I thought that was the case with all people in the world (I've had the experience of crying and tired sleeping once or twice thinking about death), but I was really surprised to learn that there are quite a few people who have never really thought about death.
I don't want to die either. I want to stay in this world as long and fun as possible.
Meanwhile, the Buddha said, “We are not going to die, we will welcome you to the Pure Land. It shows “and I will live forever,” so I'm wondering if that's the case.
I don't think anyone other than the person himself can show a satisfactory answer to my son's question. I think there is no choice but to wait until the person himself notices something or stops thinking about the problem. So, as others have said, I think it's better to just be around right now and listen as much as you can to your words and thoughts. It's frustrating, and I don't know if it's going to be hard...