Iterates over all direct child nodes of the node.  This iterates
        over all fields and yields the values of they are nodes.  If the value
        of a field is a list all the nodes in that list are returned.

def iter_child_nodes(self, exclude=None, only=None):
        """Iterates over all direct child nodes of the node.  This iterates
        over all fields and yields the values of they are nodes.  If the value
        of a field is a list all the nodes in that list are returned.
        """
        for field, item in self.iter_fields(exclude, only):
            if isinstance(item, list):
                for n in item:
                    if isinstance(n, Node):
                        yield n
            elif isinstance(item, Node):
                yield item