I've asked the question, and sought the answer -- from young children.
Phrase it like this: "Do you know right from wrong?"
You will learn from it.
Yes -- but will you learn from it?
The fact is that kids learn the difference between right and wrong from others, and not by exercise of their abstract reasoning powers (which are extremely limited).
If you're going to claim, however, that they "just know" what's right or wrong, then you are required to tell us precisely how they know it -- seeing as how they've generally got neither the intellect nor experience to come up with that stuff by their own feats of reasoning. (I think at that point you're left with some form of "mysticism," or an argument from genetics -- neither of which supports Rand's claims.)