It's easy to be taken in by our own competitiveness and forget our manners when watching our children participate in games and practices. Many of the game officials and all of the coaches of whom you will come in contact are volunteers. Others are teenagers trying to learn how to officiate at a very basic level and earn a little money in the process.
They are going to make decisions with which you don't agree. They may even make some calls that are wrong. If you feel you must criticize someone, please do it privately in a calm manner.
If we all remember that Coaches coach, Players play and Parents cheer, everyone's experience with youth sports will be a lot more fun.