Sorry to hear that, but as you've seen, life goes on. I once had two cats I was really attached to. They died a few years ago. Right after the second one died I found two 3 day old kittens under a bush. I've had them ever since and they're like children to me now. I like to think the spirits of my first two cats lives on in these two. I'm sure it's the same for your son's kitten.