This is a picture book and it says it's for children, but I wouldn't read it to a child. Reviews call it an Orwellian fable. The pig farmer, Mary, befriends the pig and then tricks him into getting into the van to go to the market. Trust, betrayal and death. Definitely not for young children. Besides being seriously weird it has disturbing photographs of individuals holding up different masks for illustrations. I don't know if you can see the cover well from the photo here, but that's a ring of piglets around the woman's neck.
Now this was a highly reviewed and very successful book, I'm just warning you that in my opinion it's not for young children despite the fact that it's a picture book.