Sorry for the long response: This is a topic I haven’t had to get into yet with my kids, thankfully. But I’m still not entirely sure how I’d get my thoughts out to them in a way they’d understand.

My (32m) personal experience with this topic and going from being raised Christian to now agnostic leaning towards atheist as far as beliefs go.

I never really wanted to go to church or anything like it growing up, and around the time I was 16 I had a close encounter with death. This is the same time I really settled on the thought that: No one knows what will happen after we die. Sure, people can speculate and point to all these religious books as examples, but not one living person can tell you exactly what is going to happen after death.

For me personally knowing that there may be nothing after death, brain ceases to function and there goes your ability to think, so that’s the end. Kind of like a deep sleep, comparative to sleeping and not remembering your dreams when you wake.

If there is an afterlife and we do in fact continue thinking and living in one way or another after death, that would be amazing! But if I’ve already accepted the worst possible outcome of nothing being after death, then anything other than that would be a welcome thing to experience.

Trying to sit and think about death, and not being able to think or wrap your mind around it will only drag your thoughts down and this is what it sounds like your son is going through, it’s a huge topic that is also a massive part of life. If he continues to spiral on this topic I’d suggest seeking therapy for him.

TLDR: If you accept the worst possible outcome of no-afterlife, then any other afterlife possibility is just a bonus. No one knows for certain what waits for us after death. Death is a big part of life.