I am very much in love with the idea of having physical play supplemented with digital learning. I have 4 nieces aged 5 to 12 and I can attest to both their love for going outside to play, and their love for technology and staring at screens. Bringing mobile gamification and learning to the playground seem like a great way to introduce and reinforce good eating habits while also relating to young people in a format that they will understand. I think that if you turned it into more of a game that would be great. Maybe a type of Lazer Tag that they could play with the design of the park. In any case, I think you're on the right track.
I absolutely love the idea! As somebody who has recently slipped off from going to the gym 6 days a week, to only going about 2 days a week, I could see this being a huge motivation for me. Since you would be selling the electricity back into the grid, I would be expressly motivated if that they translated into energy savings for me; ie, money off of my own electric bill, gas cards, or even VISA/Mastercard gift cards that I can use to make whatever purchases I want.