Too much practice doesn't make perfect. It makes overuse injuries.

For some young athletes, sports are about more than good exercise, self-esteem, and teamwork. Kids compete to be chosen for elite travel teams, hoping they're a steppingstone to scholarships, the Olympics, and professional contracts.

This pressure to play a single sport, play it the best, and play all year long is leading to overuse injuries that are taking kids out of the game permanently—before they even reach high school.

Young athletes with big league dreams can immediately learn one lesson from their sports idols: Rest!

"They all take time off," says Dr. Carlos Uquillas, a sports medicine specialist at the Cedars-Sinai Kerlan-Jobe Institute. "I tell patients that all the time: No professional baseball pitcher throws year-round. They just won't last that way."

The American Medical Society for Sports Medicine issued a warning about overuse injuries resulting from intense training at young ages. A recent study in the American Journal of Sports Medicine found kids who specialized in a sport face a 50% greater risk of having an injury.

Variety is the key to avoiding injury. In the offseason, play sports or try workouts that focus on different muscle groups. If your kid likes baseball or soccer, swimming and running are great for the offseason.

"Too often, these conversations happen after there's already been an injury," Dr. Uquillas says. "Rest periods should happen not only on a weekly basis, but year-round, including a few weeks of rest from their go-to sport."

Pain isn't part of the game. Don't ignore it or play through it.

"A lot of parents seem to think pain is just a part of sports, and you should just play through it, but that's what's causing a lot of these more serious injuries," Dr. Uquillas says.

Dr. Uquillas says parents are pushing their kids earlier than ever into a single sport, especially if they see some talent or passion early on.

Kids are especially vulnerable when they're still growing. Their bones are weaker, and the injuries can be more serious and tougher to fix. By sophomore or junior year in high school, growing is mostly done and it's safer to consider specializing in a sport.

"They're also more developed emotionally and psychologically, so they can decide what they want to do," Dr. Uquillas says.

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For every Tiger Woods and Serena Williams, there are thousands of athletes who didn't make it due to injuries or burnout.

"You have to be wary," he says. "These kids should be playing for fun and not because they want to be professional athletes someday."

Dr. Uquillas says he understands the pressure parents feel—not just about sports, but academics, instruments, learning languages, and other activities. But free playtime is crucial for kids' developing bodies and their brains. He suggests setting aside the plan and freeing up time for fun.