Kids aren’t always forthcoming about pain, and symptoms can be subtle — much subtler than limping, swelling or bleeding. To catch problems early, "parents should pay more attention to any changes, not just obvious signs of injury," says Dr. David Geier, an orthopedic surgeon and director of sports medicine at Medical University of South Carolina.

Some red flags:

Change in technique. Young athletes might make minor changes to their motion or form to work around pain. You also might notice a drop in performance level.

Difficulty sitting. Kids with knee pain might have trouble keeping their leg bent continuously — sitting in a car or movie theater, for example — and often will feel better if they straighten it out or walk around. Going up and down stairs also may hurt.

Behavioral changes. Inability to sleep, mood swings and lack of appetite can be the first signs that a child is sore, which may keep a sport from being enjoyable and possibly contribute to mental burnout.

Headaches. If a headache develops after any blow to the head — even a seemingly insignificant blow — don’t ignore it. Kids with pain that persists after a head injury should see a doctor before trying to play again. They also need medical attention for headaches that occur during or after exercise.

Unusual comments about a sport. "I don’t like pitching anymore" might really mean, "My arm hurts when I pitch." Ask questions to find out why a child feels that way.

Low back pain. Activities that stress the back, including football, gymnastics and weight-lifting, can gradually damage bones in the spine. Stretching, strengthening exercises, rest and breaks from a sport can help.