That's actually a good idea. After japan.inc stopped making the 400 - 450 "commuter" bikes they started pumping out in the late 70's, decent starter/econo bikes are getting hard to find. The toy ninjas aren't really good for that duty because of the seating position. It's hard enough to learn to ride safely without also having to learn to sit like a constipated frog.
That 'Charley Davidson' that someone in San Diego was building in TX from Chinese parts might work, but I doubt it's reliable or tough enough to get the average youngster the experience needed to graduate to a real bike.