For all the parallels between Nicholas and Nicola, I think he's essentially a different sort of character: he belongs to the picaresque rather than the psychological aspect of fiction--at least at first, he's a focal point for the creation of a world, rather than of especial interest in himself: and picaresque characters are often implausibly talented and likeable because it gets them into the next situation easily (though I have also met real people who are picaresque like this: I find them fascinating because I am essentially the opposite). And that's especially true when Forest is writing him as an 11-year-old: I suspect he's actually just a year or two too young for her skillset. He's more interesting as a character in his own right later on.