That’s a pretty vague request. Be more specific in what you are looking for. There are unlimited things that can be done to develop pitchers at the youth level. Every pitcher can benefit from drills that enhance dynamic balance and synchronicity of movement. These can be throwing or fielding drills. If you have specific things you want to work on, I’m sure we can recommend some great drills, but we are not going to info-dump our entire arsenal of drills into one forum thread. That would take a lot of time.
The biggest mistakes I see in the execution of drills is making the groups too large or getting in too many repetitions in a short period of time.
The coach can’t possibly watch the entire staff in a drill. What ends up happening is a few execute it properly, while the rest are flawed and then repeat and engrain flawed movements through repetition of an improper pattern. Keep your groups small. Make sure everyone is executing it properly. Get in as many repetitions as you can without sacrificing technique.
The best analogy I have for too many repetitions in too short a time is excessive BP. Most kids can’t put more than 10-15 good swings together without getting tired and altering their swing. Now you have another 30-40 balls in the bucket and those reps will all tear the hitter down and reinforce negative swing habits. You are better off having 3 hitters per bucket and have them go through 2-3 rotations to get their swings in. Then bring in 3 more hitters, etc.
The same is true for pitching drills. Quality before quantity. Don’t misunderstand here. Quantity is critical, but they have to be meaningful repetitions.