def _is_mutated(self):
        """
        :return:
            A boolean - if the sequence or any children (recursively) have been
            mutated
        """

        mutated = self._mutated
        if self.children is not None:
            for child in self.children:
                if isinstance(child, Sequence) or isinstance(child, SequenceOf):
                    mutated = mutated or child._is_mutated()

        return mutated
:return:
            A boolean - if the sequence or any children (recursively) have been
            mutated