Friends of ours have lost their daughter to breast cancer - and she had three children aged, 4, 6 and 12. They'd like suggestions for books that could help the children cope with their loss. They have Badger's Parting Gift and have asked for book suggestions that feature people rather than animals.
Books that helped me when my father died when I was 14 were 'Dicey's Song' by Cynthia Voigt and 'A Sound of Chariots' by Mollie Hunter. They might be suitable for the 12 year old. I read them over and over and they helped a lot. Not sure if either are in print but should be available second hand.