My oldest son is 3, and I don't think it stretches the bounds of parental objectivity to say that he's particularly perceptive.

He noticed early on, for instance, the absence of my father, who died in 2001. Figuring out exactly what happened to "Grandpa Bob" has been an ongoing project for him.

As a parent of very young children, you quickly realize what a dangerous place the world can be, and my primary task these days is to make sure my boys don't accidentally kill themselves. But on a cognitive level, there's just no shielding them from death.

My son constantly runs up against it. He notices the flowers fading in their beds and the yellow jackets giving up the ghost as cold weather approaches. He knows the shrimp he loves to eat used to be alive. He's even questioned the fate of "The Old Lady Who Swallowed a Fly." (You'll recall it wasn't the fly, but the horse that did her in.)

He recently discerned that death applies to him, too. A little shaken by the conclusion, he turned to me for confirmation: "Daddy, will I die?"

This is the moment when many parents begin knitting the safety net of heaven beneath their children, but unfortunately I lack the skill and dexterity required to spin that kind of yarn, so I had to let him know that, yes, at some point he would no longer be alive.

With tears in his eyes, he explained the part of death that most vexes him: "But I don't want to not be here."

My son doesn't want to be gone; he wants to always be here, participating in life. Me, too. For all its challenges, life is pretty spectacular. Moreover, it's all we know.

My job, as I see it, is to explain to my children the physical reality of death while preserving the sense of wonder and mystery that makes children want to discover for themselves what, if anything, life means. The best way I can think to do this is to show the boys how the infinite and the eternal mingle in the bond between life and death.

In college, I studied physics and mathematics to equip myself for this task, and I learned a few things. I learned, for instance, that the breath I just exhaled contains enough air molecules that in about 10 years' time — once that breath has properly diffused into the atmosphere — every breath taken by every person in the world will probably include at least one air molecule from it.

That's pretty amazing.

It's been nearly 10 years now since my father discovered he had terminal cancer — 10 years since I sat down on his hospital bed and he pulled me close and whispered into my ear: "You're my strength, Mike."

Today, I literally breathe in those words every day, and so do my boys.

That's one way of seeing the physical reality of death, and that's one way I will explain it to my children.