Guan,
But it does not. They are all peers. One is just the "original" I think cr_child_rel is for compound content items where the children are parts of one big item. So a "page" might be made up of several content items. So for a compound item each translation could would have it's own children.
Joel,
The issue is that someone might want to know what language an item was translated from. I think you are correct that this is probably more application specific and does not need to be part of this TIP.