I'm the wrong person to answer the motivation for 2 hour runs part because for the most part we don't go that long. As for the motivation part some of it has to come from within if they understand on some level what they are doing and why (different levels of that for different kids)I've found that works. Also we are fortunate to have some trails and parks where we can do runs and I think the change in scenery does make it more of an adventure and less of a monotonous struggle. We've also done brunches or picnics after long runs if you really need a carrot and stick approach, although that isn't why we do them.