Returns set of hosts that belongs to a group including those that belong
        indirectly via inheritance

def children_of_group(self, group: Union[str, Group]) -> Set[Host]:
        """
        Returns set of hosts that belongs to a group including those that belong
        indirectly via inheritance
        """
        hosts: List[Host] = set()
        for host in self.hosts.values():
            if host.has_parent_group(group):
                hosts.add(host)
        return hosts