Kilmoulis are British fairies very much like the brownie, only specific to mills.
Like the brownie, they pick a home (in this case mill), pick a family (the miller's family), and then make themselves useful, usually cleaning up and (since, again, mill) working to make good quality flour. They also occasionally make stuff worse by wrecking up the joint and making a mess, but usually the flour they've made is so good that nobody minds.
Oh, also they have no mouths and need to snort their food up their gigantic noses. But other than that, yeah. Just like really ugly brownies.