Have you tried google sketch up... it can create 3-d images, I haven't tried it yet so don't know how difficult it would be.
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I would like to do a package design project with my fourth graders. Our computer lab has Kid Pix but that won't be good for this project. Do you know of a free draw/paint/text software for either the MAC or our IPADs (I will have to find out if we can print from our IPADS)