Yes, he would know, because he did, and it's hardly a shock that he would look so smug about it, at that. Childermass refrains from rolling his eyes since he actually is grateful for magic's return. That doesn't mean, however, that he won't point out, "And left me far too many new magicians who also all think they know better than I do, for that matter."

With no great library of books on magic to fall back on or to help teach them with. It's an interesting dilemma, to be sure, though not one he has to worry about for now. The carnival is outside of that time and space, so it'll stay until he can get back to it.