Well, humans don't like to hurt people who we see as similar to ourselves. And when we learn random information about someone, we tend to see them as a person like us. Humans do not normally extend this honor to strangers beyond a small circle or Monkeysphere. But we still don't like to hurt people when we see them as people. And science tells us pretty early on that yes, those people we don’t know can feel emotion just as strongly as the ones in our Monkeysphere. (Technically we can't prove that anyone has feelings, but we've just established that all non-sociopaths accept some others as feeling humans.) So reason combined with instinct makes me feel bad about hurting people. These two much-maligned factors together give us morality. It doesn't work if someone lacks the instincts in question, but we have guns, police and martial arts for just such an occasion. (And I doubt many sociopaths would listen to us no matter what argument we make for morality.)
But plenty of societies have failed to apply this principle in the correct way (meaning, the way we'd like). Don't we need more to ensure that we pass this morality on to future generations? Well, we have other instincts to use. Children don't like to disappoint their parents. Humans in general don't like it when society shuts them out. It seems to me that combined with the Monkey principle, these facts remove the need for any mention of deity in moral education. I don't think we even need to go beyond the empirical facts. At worst, we can tell children a partial truth like, 'I view it as wrong to hurt people'. I would actually stick to the truth even more closely than this. Either I would tell children (truthfully) that I don't want them to hurt people, or I'd mention that my personal rules have exceptions and offer (truthfully) to discuss them at a suitable time.
You may well see this as impractical. I did feel uneasy about my armchair advice on child-rearing when I typed it. But here we come to an interesting fact. I discovered this while researching my philosophy, but I'd forgotten it until I had to defend my program. According to REBT, a non-chemical therapy that works better than others in outcome studies, viewing morality as a law of the universe does not lead to sane behavior. Rather the opposite. REBT therefore encourages us to view actions and morals through the prism of "rational goals", which can overlap with "True Will" as I define it. More on this in my next post, where I try to bring it all together.