My husband died 2 years ago from cancer. Our children were 10 and 7 at the time.
Books were OK, depending on what they were about. Movies or music were better because they took less effort, and energy becomes very valuable. If they are advice about death, dying, or alternative treatments, it gets really old, really fast. (Everybody wants to tell you what you should eat, what magic drink there is, the magical prayer that prevents death from cancer, etc... when you have cancer)
The best thing you can do is spend some time with them making some good memories, let them share on their terms (let them set the boundaries), and be available as a friend.