Has anyone come across any good textbooks / training manuals for trainng young athletes?
Here you go. Have no idea what age group you are targeting but this is a good place to start. I like Drabik's book a lot and also think Myslinski (sp?) has written some good articles on the topic. You will have to search them on the site.
Also, the Bompa book is interesting.
Basically, a lot of everything and very little specialization. Let them develop overall athletic abilities.