I am mostly in agreement with GBM, but would phrase it a little differently, from a slightly different perspective. My son also throws from the low 3/4 arm slot, and he features a Curveball (and a very nice one).
I'm of the school of thought that the amount of velocity on a pitch, and the amount of rotation on the ball, are derived from the set of the wrist and forearm. When the hand is set directly behind the ball -- you have a Fastball (maximum velocity, least amount of "side" rotation).
-- 1/8 turn of the palm in and you have a Cutter
-- 1/4 turn of the palm in and you have a Slider
-- 1/2 turn of the palm in (Karate Chop) and you have a Curveball
-- 1/4 turn of the palm out and you have a Change
-- 1/2 turn of the palm out and you have a Screwball
We're of the school that says "set it and forget it". My son has learned to set his grip and forearm in the glove, and just to "throw a fastball". Ideally, all of these pitches should be thrown with Fastball mechanics and arm action.
My understanding (and testing) is that the Slider is tougher on the young arm because it requires more strength to hold the proper arm position throughout the delivery. Kids often wind up twisting their arm during the delivery itself, which is what berings on the higher probability of injury.
Results: Southpaw Son features a CB that breaks late, with a 11-5 or 10-4 break, that runs about 10-12 mph off his FB. It makes for a great breaking pitch, and his mechanics are vritaully identical to his FB, making ti very hard for hitters to pick up.
Hope this helps.