PlayPump failed, as so many others, because children do not make good horses. Countless projects in many fields have attempted to "harness" children for energy. There was the soccer/football generator (https://www.youtube.com/watch?v=oeb2fyHKirQ). I've even seen attempts to install power-generating floor tiles in English schools (https://www.youtube.com/watch?v=_9AZxB55xjI). We think we can tell children what to do, use them as beasts of burden, but they are not a reliable power source.