Exactly. You can save them and send them to Earth on the machine you're modeling, and save the kmz's and just pass those around for privacy. When you select "Place Model" in SketchUp, it'll send your model to Google Earth, only on that machine, and put it into Temporary Places->SUPreview1. If you do more buildings, they can be SUPreview2, 3... then right click on Temporary Places, and select "Save Place As..." and save the kmz. Now you can share it only with the people you want, buildings and all.
When you feel OK with it (and you will), you should submit to 3dwarehouse, and give the kids some credit for their efforts... you should check out the Cities in 3D program at http://sketchup.google.com/3dwarehouse/ and there's more, too, if you look around.
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