From a researcher at McMaster University, we learn that Slow Balls Take The Swing Out of Young Ball Players (via kottke). It turns out kids have a harder time seeing slow motion than fast, tending to see slow moving objects as stationary.
I’ve definitely found this to be true when pitching for Henry. He can’t reliably hit really fast pitches, but has just as much trouble with really slow ones. There’s a sweet spot in the middle where he can hit most every good pitch (and a lot of the bad ones).