Hmm... my word choice of "excellent" was unintentionally misleading. I didn't want to imply that good fiction was a fast way of building vocabulary; you could be much more efficient with flashcards. But if a child's willpower isn't at the "happy to study flashcards in place of entertainment" point, then it's still worthwhile to find activities which are entertaining but also educational, then save the flash cards for subjects where you can't find such substitutes.