It's not, of course, that he came up with some brilliantly convoluted theological argument; he's bright and all, but he's just an ordinary kid, and far from being steeped in theology, he's been kept well clear of it. He has a variety of religious viewpoints around him, from a quite religious sister to a strongly atheistic father, but none of us proselytize him - we are all letting him be until he expresses an interest, and then he will be free to make up his own mind.
No, what he did was demonstrate the basis of morality, by insisting that he wanted to invite all the kids in his class to his birthday party, even the ones he didn't know, because "it's no fun not to be invited." Simple as that.
That, my friends, is where it all comes from. Not from Big Sky Daddy standing over you with a cat-o-nine-tails in one hand, a ticket to Candyland in the other hand, and a stone-clad rulebook in the gripping hand, but from simple human empathy for how others will feel.
"But-but-but... What's to stop an atheist from doing anything, raping and killing included, if there's no Cosmic Cop? How can you have absolute morality without an absolute master telling you what's moral?"
The answer's right there; my son did the Right Thing not because of any fear of punishment - he was actually being encouraged to limit his guest list, not expand it - because he empathises with his fellows, and cares about how they feel. That's not new, or deep, or unusual, by the way; every normal human child cries when hearing crying, laughs when hearing laughter. Most of it's inborn, and a judicious application of reward and punishment (saying "What a good boy!" and "I don't like it when you act that way." is sufficient in most cases) produces human beings who
behave morally without the necessity of either coercion or reward.
As for absolute morality - there isn't one, if by that you mean a set of absolute rules which, if followed absolutely, are absolutely always moral. Absolute rulebooks usually end up causing misery and resentment and hatred, and by their fruits are therefore evil. Guidelines are a
much better way to go, and every normal child understands the most important one instinctively; do unto others as you would have them do unto you. (Am I using enough Biblical language to get through here? There's good stuff in there too, you don't have to get stuck on the
sexual hangups and bigotries of the authors.) It's no fun not to be invited, so invite everyone you can; that's a good moral decision, reached by a kid applying a very simple principle - not blindly
following a rule, but using his empathy and common sense to decide how to behave. If resources were too limited to invite his whole class (luckily not the case), then he'd have to figure out a fair compromise, but again, he'd be figuring out a realistic moral choice without the need for supernatural supervision.
If people concentrated less on trying to divine some absolute set of stone rules, and put more effort into figuring out how best to be kind and fair, even if that involved adapting their responses to fit specific cases, this would be a happier, more harmonious and yes, more moral
world. Perfect, no; people will always find a way to talk themselves into mistakes, even if you do try to predetermine their every allowable move. And no, I am not recommending anarchy; a society needs rules, laws, and enforcement mechanisms for them, and the decision of what to
allow and what to outlaw always involves moral as well as practical concerns.
None of that requires a ghostly overlord, though; simple human empathy and common sense are all that is needed. Don't hurt people. Make their lives better and happier where you can. If they're not hurting others, leave them alone.
Is that so hard?