Return tuples for all child GO IDs, containing current GO ID and child GO ID.

def get_all_child_edges(self):
        """Return tuples for all child GO IDs, containing current GO ID and child GO ID."""
        all_child_edges = set()
        for parent in self.children:
            all_child_edges.add((parent.item_id, self.item_id))
            all_child_edges |= parent.get_all_child_edges()
        return all_child_edges