I like the scales idea. I've been working with WOA (http://www.easyway2health.com/woa-system.html) for a while to develop something similar; the scales don't have to tell you your absolute number, just whether you're moving in the right direction. For many people who've struggled to lose weight in the past, this could be a good motivation tool.
I'm a little unsure about the organic route; I worry it would dilute the message. We're trying to get people who are likely to be in lower-income brackets involved and I could see this as a real hurdle for uptake. Is there a reason you feel organic food specifically would be beneficial?
I can suggest a few ways to simplify the scheme so that children can take part:
1. Rather than a 'winner takes all' approach, what about staggered targets? If the family gets a guaranteed reward for hitting certain targets (10lbs total, 5% loss, 10% loss, etc) then the weight lost 2. Ensure there are hard 'top' amounts someone can lose. So no-one can lose 20% of their initial weight; this would help reduce the pressure on the children to lose weight fast. 3. This one takes it out of your original idea, but - no deadlines. If this was to be used it obviously would reduce the gamification appeal, so I'm not certain it's right, but again it would reduce the pressure for speed, my biggest concern with Biggest Loser events.
I like the way this is evolving- do invite me over if your work with Logan gets going!