If your child isn't already participating in organized sports you need to definitely get them started right away. It's a lot more than just sports that they are participating in. 

First off organized sports are a great way to stay in shape. Find a sport that they will enjoy, don't just push them into football becuse your a football fan. Most people tend not like to straight up exercising, but playing a sport you enjoy is exercising in disguise. It will keep your children living a Healthy lifestyle without even having to force anything upon them.
Organized team sports is one of the earliest ways were a child has to be able to use their team to succeed. The earlier they can get in the habit of using others around them the easier this will become in life. One day they will be all grown up and looking for a job. Not many jobs out out their do you not have to use your fellow co workers. Sports is a great way to get in the habbit of being a team player and not just all about yourself.
Many people these days are just so used to getting things handed to them they have no idea what work ethic is. Organized sports will show your child how to compete and what it takes to be successful. Success comes from hard work and effort, doing the little things are just as important as the big ones. Just worrying about scoring a goal or getting a point isn't enough, you need to be able to work hard and be determined to accomplish tasks. Once again in the job market many employers admire hard workers. If your willing to go the extra mile you will get a lot further in life than the guy that isn't willing to. 
Last but not least every parents dream is their child in the big league one day. This will never happen unless you enroll your child in one of the many sports that is available out there. Never let anoyone tell your child that they can't make it big, because they can if they want it bad enough. Hard work and sacrifice goes along way, embrace the fact they want to go big.