Knucklecurve,
A very good question and some very good answers by svd16u and like2rake. There are a lot of different ways to go with this. I think the most important tool a player can have is the ability to hit the baseball. If you can generate runs there will always be a spot on a team. But what if that player is a pitcher? The least important part of his game is the ability to generate runs. So in reality, we have to look at each situation differently. I think the best way to approach this is to properly evaluate a young player and determine his strengths. His strengths (or weaknesses) will normally guide him to a particular position. Once you have determined what position fits him best, hone those skills to make him the best you can. I’m not advocating to you to ignore any aspect of his game, but I also don’t think you should compromise his strong area(s), by devoting too much time on trying to correct his weaknesses. As he develops, things could change but you have to go with your instincts during the pre-high school years. Most players will have a weakness that will limit their effectiveness at a particular position later on in high school and college. The earlier you identify that weakness the better off your son will be. For my son it was foot speed. His weakness limited him to the corners of the infield, pitching, and/or catching.
Again I think hitting is the most important tool with arm strength running a close second. In order to improve either (or both) of those, the player has to have a good work ethic. In order to implement those tools in a game situation he has to have the proper mental approach to the game. Tall order but it can be done!
Best of luck,
Fungo