Never trust a trailer or a dust jacket. I don't think that's supposed to be his real family, if I remember the interview correctly.

You can read the text of the article I mentioned here, but here's a relevant snippet:

Early indications are that the film will be very different from the dreamy and timeless novel.

In the film, Will Stanton is 13, not 11, and he is American, not British. Screenwriter John Hodge first looked at The Dark Is Rising many years ago. At that time, it just didn't seem like the right project for the man who wrote the screenplay for Trainspotting, a gritty film about heroin addiction. Hodge didn't like fantasy anyway.

And even when he approached the book 10 years later, Hodge found many problems. First of all, he thought, even though the book was written more than 30 years ago, the premise of an 11-year-old English boy who finds out he can do magic seemed too familiar.

"One of the things I didn't want it to be confused with was Harry Potter, because I just think the world doesn't need another English boy involved with fantasy adventures," he says.

Hodge felt that Will would be more understandable if he was experiencing things as an outsider, as an American living in Britain.

As for Cooper's story, Hodge says that "a lot of it would have to go because it was written in this quite lyrical, poetic, kaleidoscopic fashion." He also says the novel, as written, proved difficult in other respects: The action doesn't take place in fixed locations and, he says, Will "doesn't really do very much."

But further on in the article it's implied that Cooper's own feelings may be similar to yours.