Returns whether a key is strictly a child of another key.
        AoT siblings are not considered children of one another.

def _is_child(self, parent, child):  # type: (str, str) -> bool
        """
        Returns whether a key is strictly a child of another key.
        AoT siblings are not considered children of one another.
        """
        parent_parts = tuple(self._split_table_name(parent))
        child_parts = tuple(self._split_table_name(child))

        if parent_parts == child_parts:
            return False

        return parent_parts == child_parts[: len(parent_parts)]