This can be a difficult story to go over with children. It is easy to make God look "unreasonable" with this story. I've heard the story quoted by people as an example of how "ridiculous" the Bible is, by people who haven't taken the time to understand. And I've had some Christians write me with their discomfort about sharing the story with their child. But I think that presented properly, it can be a very valuable lesson to children.
I've added a lot of explanation to the children's version of this story to help children understand why God would favor Abel over Cain -- I would make sure to read a children's version of some sort before reading the King James (or other) Bible version. The first time I told the story to my oldest daughter, she commented that she was going to be a shepherd when she grew up because God likes shepherds more than farmers -- not quite the point, honey *smile*.
- The children's version of the story
- Lesson 1: Why does it matter?
- Lesson 2: Am I my brother's keeper?
You can focus on just one of the lessons or on both of them. If working with younger children, I find Lesson 2 a bit easier for them to understand.