You might be thinking of Mama, about the two girls living in the woods with the ghost. It was a short film that Del Toro saw, then he produced the big picture (both were directed by the same guy).
P.S. - I got it from Redbox over the weekend. Neat concept, but disappointing. It's PG-13, so it felt like a basic SyFy channel ghost movie.
So stoked to see this, for all the reasons already brought up. Del Toro is an awesome filmmaker and "Transformers vs. Cloverfield" has major entertainment potential.