<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_children(self, name):
 r""" Get the children node names of a node. :param name: Parent node name :type name: :ref:`NodeName` :rtype: list of :ref:`NodeName` :raises: * RuntimeError (Argument \`name\` is not valid) * RuntimeError (Node *[name]* not in tree) """

        if self._validate_node_name(name):
            raise RuntimeError("Argument `name` is not valid")
        self._node_in_tree(name)
        return sorted(self._db[name]["children"])