Here's a couple of pages of really super books for and about youth and the wonderfullness that is baseball:
http://www.uta.edu/english/tim/baseball/juv/hjuv.html
and
http://www.uta.edu/english/tim/baseball/juv/bjuv.html. Also, one of my favorites,
CARL DEUKER, HEART OF A CHAMPION
Three more great ones are Choosing Up Sides, The Boy Who Saved Baseball and Over the Wall by John Ritter
http://www.johnhritter.com/