Sorting posts by parent/child fields?

This is a long shot, but somebody out there might have an idea on this.

I have setup a site with several custom post types with parent/child relationships among them. When I query a list of one of these post types, it’s pretty easy to get the IDs of the parents and children to display any attachments or fields associated with those parents and children as well. But I’m wondering if anybody knows of a way to sort the list by a field from a parent or child rather than just the fields associated with the post type I’m querying?