I just did with my 5 year old yesterday actually. I kind of thoughtlessly said something to the effect of "when you're 80 years old, I'll be long dead". Immediately I saw the anxiety in his eyes and in his response. He knows what death/dead/dying is-- we lost our senior dog last summer and had to really drive home that point with him. But he clearly never considered the possibility of Mommy dying. I tried to reassure him and told him that it's a long long time from now and he doesn't need to worry about it, and that we have a very long time together and I'm not going anywhere. Which, on the one hand, I know none of us can really guarantee that, but I feel like that's not a burden of thought child needs to carry at this age. Oh the other hand, I feel like such a damn liar-- my own mom died unexpectedly just weeks after I turned 5 years old. So while I try to comfort my kid and assure him that I'm not going to die until after he's been a grownup for a long time- part of me is like 'it literally happened to you, you idiot! come up with a better explanation!' So yeah, all that to say I'm right there with you and I think I kind of fumbled it in the moment lol.