'Training For Young Distance Runners' is the best book I've come across for anyone interested in coaching young runners. In fact, I wish a lot more coaches would read this book, because it covers more than just training the physical, but also talks about running technique, basic physiology, adaptations to training, different racing strategies and the importance of motivation. Overall the training philosophy is sound, as it breaks training down into different phases. It covered the technical aspects of running without getting too technical, touches on specific components of running and training, and also steps back and looks at the bigger picture in regards to planning ahead and assessing results.
I can't recommend this book highly enough. If/when the time comes for me to be in a position again to coach young runners, I will use this book as a constant resource.