The Australian Open began this week. The best tennis players in the world are competing for the first major title of the 2012 season.

Actually, the professional tennis season started January 1 with another tournament in Australia. Of course, the tennis season is so long it almost never ends. Tennis pros play tournaments every month of the year except December.

The long season means several things. First, tennis players get hurt — a lot. Top-rated players Rafael Nadal, Roger Federer, Caroline Wozniacki and Kim Clijsters were all reportedly suffering from nagging injuries at the beginning of the Australian Open. During the first week of the United States Open last year, a record 18 players could not finish matches because of injuries or other ailments.

Second, tennis players quit their sport early. It is common for tennis pros to retire from competitive tennis when they are still in their 20s. Jim Courier, who retired at 29 after winning four major titles during the 1990s, told newspapers last fall that he would have played at least three more years if tennis had a shorter season.

This is a good lesson for kids as well as for their parents and coaches, because kids’ sports seasons are getting longer. Some kids play basketball or soccer year-round. Other kids swim competitively every month of the year. There are more fall baseball leagues and spring football leagues.

One sport all year long is not healthy. (Robert Neubecker for The Washington Post)

And, no surprise, just like pro tennis players, more kids are getting hurt. The American Association of Pediatrics (a group of doctors who take care of kids) warned in a 2007 report that children are getting hurt more because they play too much sports. The report also said more kids, like tennis players, are getting burned out from the pressure and are quitting their sports.

So what should kids do to avoid getting hurt and burned out? The doctors recommend that athletes take one or two days off from competitive sports every week. They also recommend that athletes take two to three months off from their main sport during the year.

Kids should stay active, and they should do that by playing more than one sport. Let’s say you love baseball and want to be a Major League Baseball pitcher. Don’t focus on pitching all year. Play soccer in the fall or basketball in the winter. That way you can stay in shape, have fun and not use up your pitching arm.

The same goes for other sports. If your coach says you have to play year-round to become good, tell him no one is very good if she is hurt.

Fred Bowen writes the sports opinion column for KidsPost. He is the author 17 sports books for kids. His latest books are “Quarterback Season” and “Real Hoops.”