Some day, your child will look back on the summer evenings spent playing catch with mom and dad. Get involved in your local League. Little League is run on a volunteer basis, and they can use all the help they can get. Anything you can do to pitch in will make the League run more smoothly, and will help all the kids, from helping out at tryouts, to scorekeeping or field preparation, to umpiring. And, the Leagues provide all of the training anyone needs.
Different coaches have different philosophies.
Some believe in having players play all positions, some want players to become good at one. For heaven's sake, show up for the games AND the practices. Most people wouldn't dare to not show up for work and still tell the boss what's wrong with the company, but they will turn around and do just that with their childs' coach. This is what the kids should be learning. If you don't agree with an umpires call, keep it to yourself.