MacLobo - The following is the opinion of a young catcher's dad, and youth coach (currently 12U)...
Youth progression...
1. Throw strikes - Especially at the younger ages, the most effective thing a pitcher can do is not walk batters, and give their catcher a good chance to catch the ball. This, alone, is a gigantic game-changer for 8U and 10U.
2. Improve velocity - Once there is consistency with staying in the strike zone, increasing speed will improve effectiveness. However, if the BB count increases, it's a step backwards.
3. Change-up - With a consistent fastball, a reliable change-up improves the effectiveness of a young pitcher dramatically.
4. Improve location control - Having the control to keep the ball off the center of the plate reduces the opportunities for quality contact.
5. Movement pitch - Drop, screw, curve. Pick one and master it.
6. Riseball
The other school of thought is switching #1 and #2. Learn to throw it as hard as you can, then when you have mastered your mechanics the location will naturally follow. The reasoning is that if you aren't throwing it as hard as you can, when you start to do that it throws things out of whack. I'm not saying either is right or wrong, just that there is another school of thought.
Re: Pitch speeds. Yesterday at my daughters group pitching lessons she stayed to watch his "level 2" class which is good control & 40+ mph speeds. In the class all the girls speeds were radar gunned (JUGs) and they were throwing 40-48 mph. He asked them what grades they were in and the youngest was in 5th grade, oldest 7th (so they were all older than 10u). We didn't stay for his "level 3" class which is 50+ mph so I don't know if there were any 10u there, but I seriously doubt it. All the girls looked at least 12U, most 14U.