Children passage

        :rtype: str
        :returns: First children of the graph. Shortcut to self.graph.children[0]

def lastId(self):
        """ Children passage

        :rtype: str
        :returns: First children of the graph. Shortcut to self.graph.children[0]
        """
        if self._last is False:
            # Request the next urn
            self._last = self.childIds[-1]
        return self._last