I have read the book, and I loved it, but I have to say I would not give it to a very young child. It's a twist on The Jungle Book, but where Kipling starts with the tiger chasing a toddler in the jungle, Gaiman starts with a guy with a bloody knife searching through a house where he has just killed the toddler's parents and older sibling.
Of course, kids these days are much more inured to gore than some previous generations, but still, that opening scene creeped me out. I would think a kid would have to be ten, at least, to read it without getting nightmares.
FYI, The Graveyard Book is available on the Kindle for $9.99, and comes with illustrations intact. Also, the movie version of Coraline is coming out soon.