[U of M Sam]

Not sure what level games your umps will work although here are some of my BASIC coverage ideas (you decide order and additions for coverage):
Plate and field ump positions; proper mechanics (strike, out, fair, foul, etc); personal appearence (uniform or what you authorize-I don't like sweat pants, shorts, "goofy" tee shirts, etc as they display poor appearence); fair/foul balls (position of ball/not player) and of course all rules in general; how to deal with loud coaches/crowds; being consistant with calls and not making calls too quickly (I was taught: see it/process it/call it).
I could go on and on as I have conducted some clinics for Little League umps ages 11 thru 17.
General suggestion: Get them excited about calling a proper and professional game (be confident not "cocky").
It is great to see youngsters wanting to learn how to umpire (I am always looking to improve my umpiring skills).
Hope this helps!