In my opinion, the two key components that a baseball player needs to grasp in order to be successful at the plate are:
2. pitch selection
As a little league coach, you can help these kids with their timing right away, even at a young age. I wouldn’t worry too much about pitch selection until kids reach the 14/15U level.
How to Improve Timing
During practice you need to give your baseball players plenty of opportunities to hit a moving baseball. Don’t get too caught up on tee drills for too long. Tee drills are good for mechanics, but mechanics aren’t worth anything if these kids can’t get on time. So make sure you have a nice mix of tee work and thrown ball — be it underhand, overhand, fast, slow, whatever it may be… challenge these kids to learn how to get on time and learn how to read the baseball that is traveling towards them and when it is they need to start their swing.
At the little league level, kids should be pretty aggressive with their swings. Most hitters at this level do not understand the strike zone and pitchers are typically quite wild, so please encourage these kids to swing aggressively. I’d rather have them swing at everything and miss then take pitches and never learn how to get on time.