It turns out there's a series of children's novels, and they've gotten good reviews on Amazon. What they are not, however, is the same as the movie. After a bit of research, it's very clear to me that the movie was more "inspired by" than "based on" the books.
There is common ground between them, but if you changed the names of the movie and its characters, I suspect the only significant things they'd have left in common is the presence of vikings and dragons. I have not read the books, so there may be subtle similarities that I am not aware of, but it really does sound like they're the apples and oranges of family friendly viking-themed dragon fiction (a genre I am certain is massive in stature).
I find this interesting, as book fans have historically been strongly opposed to movies that deviate heavily from the source material. There are Harry Potter fans who foam at the mouth with rage over the general lack of house elves in the movies and Lord Of The Ring fans who want the head of Peter Jackson, but those movies are guilty of very minor divergences relative to the HTTYD movie. Given the overwhelmingly positive reviews of the HTTYD movie, I wonder what fans of the books think. It also makes me wonder what the author of the books, Cressida Cowel, thinks.
Of course, these might not be like the Harry Potter books with readers of all ages. If it's mostly just kids reading them, I doubt there'd be as much fanboy rage in the face of unfaithful adaptations. I've also never seen a bookstore overflowing with people as a result of a HTTYD book release or people getting lynched for revealing HTTYD spoilers. Nonetheless, there's probably someone, somewhere out there who is gritting their teeth with rage over this movie.
Personally, I liked the movie as it was, and I'm glad they deviated from the source material as much as they did. It's a little weird to be saying that. I'm generally okay with movies deviating from their source material in order to make movies that, frankly, don't suck. What I usually do want to stay faithful, however, are the themes and the characters, and it doesn't sound like HTTYD did that.
That said, the movie is still awesome, and I still plot to see it in 3d.
