I'm a librarian who loves anime, manga, and reading a wide variety of genres.
If Nuin never appeared in the series again, I'd be happy. He's a little monster. I'm pretty sure Owens is aiming for an "aww, such an energetic little tyke!" response from readers, but him being on his fourth nanny because he's such a terror is not charming.
This post is inspired by every brief mention of him in this book, as well as what I remember of him in the previous one. As weirdly adult-like as Vinni is, at least he doesn't grate on my nerves.