can be alarming to people, esp kids. This is the main reason I did not become a doctor, I can't stand watching pain in others. So I do things this way instead

Chemar, your son has great qualities, and obviously Moonshadow's suffering is moving him. And it might result in his choice of career, etc later in life. You need to tell him, that the kitten, does not understand this however the same way. All he needs now is comfort/patience/safety. Channeling this frustration into action, is the best way to cope...like helping MoonShadow to find his litterpan, find you (by putting clothing with your scent on it (not clean) around to guide him), etc.

I'd like to warn you though about "purring". And others here too.

We had a cat who had cancer (thyroid cancer that spread to her lungs). It was about 25 yrs ago, before thyroid disease was understood by vets in cats.
So there was a delay in diagnosis (she too had seizures). We had surgery for her to remove the tumor, but it was too late. We kept her comfortable and the vet said to bring her in if she showed distress and he would put her to sleep.
She lived about 6mos longer, and when she started bleeding from the ****, I took her in. She purred the whole while, and when I remarked on it to the vet, he said cats purr when ill, and it does not always mean comfort/love. It is more like a "help me" signal. So he would not let me be with her when he put her down, I was crying too much. I still can hear her purring away...

I found a really interesting article on purring:
http://www.animalvoice.com/catpurrP.htm
This article gives statistics on surgery and complications. Which is helpful to see also.

As far as seizures go, animals can have them anytime. It is just important to keep them safe and calm when they come out of one..they are disoriented.
I sent you an email about Taurine, Chemar. I think this is a viable thing to
consider, since your kitten is a runt..and may have missed nutrients from the mother.

Young mammals have plastic brains, meaning injury can be overcome with time. I am hoping this will be the case for you.