I'm a fan of a rise, drop, change combo... So all my pitchers start learning the rise when they're about 10 or 11... Will actually start throwing the rise by 2nd yr 12u. I have 3 freshman pitchers... All are high 50's to 60, all have a rise, and all are their teams Varsity Ace.
Many will scoff at the idea of teaching a rise to such a young pitcher. However, if you have the discipline to throw the rise it makes the other pitches that much easier. It is a great practice to expose young pitchers to multiple pitches. But you need to manage expectations that the end game is to find what works best and then work to perfect your best pitches. When it is all said and done the mechanical aspect of pitching is learning to make the ball move and end up where you want it. I teach pitchers not to think in terms of rise, screw, curve, and drop. Just make the ball do what you want. Visualize the movement and location then send it.