AssetPreview on Object children

Hey, I'm making an editor extension and want to show the "icons" of objects. I've picked [AssetPreview.GetAssetPreview][1] to do this. At one point in my script I've used it to iterate over all prefabs in a folder and it worked like a charm. Now, however, I would like to show the icons of all children of a gameobject. That means it's a normal gameobject in the hierarchy. Passing the children to the function merely returned null, so I assume I would have to get the "prefab" equivalent of the children. How do I get that and correctly use it for the function? Thanks in advance, Chelmney [1]: http://docs.unity3d.com/Documentation/ScriptReference/AssetPreview.GetAssetPreview.html