@abc.abstractmethod<EOL><INDENT>def add_child_vault(self, vault_id, child_id):<DEDENT>
pass<EOL>
Adds a child to a vault.

        :param vault_id: the ``Id`` of a vault
        :type vault_id: ``osid.id.Id``
        :param child_id: the ``Id`` of the new child
        :type child_id: ``osid.id.Id``
        :raise: ``AlreadyExists`` -- ``vault_id`` is already a parent of ``child_id``
        :raise: ``NotFound`` -- ``vault_id`` or ``child_id`` not found
        :raise: ``NullArgument`` -- ``vault_id`` or ``child_id`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

        *compliance: mandatory -- This method must be implemented.*