Ally Carr was learning how to slide into home plate this spring when she tore the meniscus in her knee. She had to have surgery to repair the tear and missed much of the season.

The 16-year-old softball catcher at Maret School in Washington hopes to be fully recovered in time to play volleyball in the fall.

More than 38 million children and teens play sports in the United States each year, according to Safe Kids Worldwide, and it's taking a toll. About one in three kids playing team sports is injured seriously enough to miss practice or a game. Those who, like Ally, play multiple sports that put pressure on the same body part are at an increased risk for injury.

Ally's mother, Kate Carr, is president and chief executive of Safe Kids. She says Ally is trying to condition her knees to better withstand the pressure that volleyball and softball put on them.

Her organization, which works to prevent childhood injuries, is trying to raise awareness of youth sports injuries and teach children, parents and coaches how to prevent them or minimize their effects.

"We [need to] begin to help our children understand that if you want to have a lifetime of being active, you have to protect your body while you're young," Carr said. "If you don't, it will either limit your ability to play this sport that you love or it will cause a lifetime of damage."

Here's what experts say about some common sports risks for children and how to recognize, prevent and treat them.

CONCUSSIONS

Causes: A direct blow to the head or a hit to the body that causes the head to jerk back quickly can result in a concussion. Gerard Gioia, chief of neuropsychology and head of the Safe Concussion Outcome and Recovery Education Program at Children's National Medical Center in Washington, said it's like an injury to the software system of the brain.

Signs and symptoms: Loss of consciousness happens in fewer than 10 percent of concussions, Gioia said. If a child appears confused, stunned or unsure about what she is supposed to be doing, she might have a concussion, Gioia said. Symptoms also include headaches, a feeling of pressure in the head, dizziness, blurred vision or feeling like your head is fuzzy or foggy.

"When they raise those questions or symptoms, then we invoke the rule 'When in doubt, sit them out,' " Gioia said. "Remove the youngster from playing, let the parent know, and seek medical attention immediately."

Gioia and his colleagues have developed a smartphone app called Concussion Recognition and Response to help coaches and parents evaluate athletes after a blow to the head.

Treatment: If the child's headache is getting worse or she is not responding to questions, has trouble recognizing people, is slurring her speech or loses consciousness, go to the emergency room immediately, Gioia said. If the child is coherent but not feeling right and having some symptoms, call your pediatrician.

There is no set treatment for concussions that will fit all children, Gioia said, but parents and coaches should manage the child's activity level to give the brain time to heal itself. After a concussion, a child needs rest from physical and mental activities, and a gradual return to normal, as long as it doesn't aggravate her symptoms. If something does make symptoms worse, stop that activity.

"You have to figure out that sweet spot of how much activity you can tolerate without worsening your symptoms," Gioia said. "That's where careful management comes in."

Prevention: Gioia said parents should advocate with their coaches and youth sports organizations to follow the safest procedures possible. Many youth sports have altered their policies to increase safety, Gioia said. Football players are taught to tackle with their shoulders instead of leading with their heads, for example. Teach your child that it is not a matter of winning at all costs and that safety should be the top priority.

HEAT ILLNESS

Causes: Extreme temperatures, particularly when combined with high humidity or intense sunlight, can interfere with the body's normal ways of regulating temperature, said pediatrician Stephen Rice, who co-authored the American Academy of Pediatrics' 2011 statement on heat sickness in children. Heat illnesses, including heat cramps, heat exhaustion and heatstroke, occur mostly outside and during the summer but can happen anytime or anywhere, Rice said.

Signs and symptoms: Children who are getting overheated might look flushed or feel lightheaded. Heat illness can also cause dry mouth, fatigue, a decrease in performance level or attention span and excessive sweatiness, Rice said. When humidity is high, sweat can't evaporate. That prevents the body from cooling.

Sweating is "really the best method of cooling we have," Rice said. "If you grab a towel and keep wiping yourself off, you've lost a chance to cool off. It's not the production of sweat but evaporation of sweat that cools you."

Treatment: Get the child to the shade as soon as possible, Rice said. Coaches should be prepared to cool someone down rapidly if necessary, including having cold, wet towels and washcloths and ice packs to apply to the child's neck, armpits and groin.

Start the cooling process immediately, Rice said, even if you are calling 911. Don't wait for medical help to arrive.

Prevention: Drink plenty of water before and stay hydrated during physical activity. The AAP recommends that children ages 9 to 12 drink three to eight ounces of water every 20 minutes. Adolescents should drink 34 to 50 ounces of water an hour while they are exercising in the heat. Encourage children to drink water before and after practices or games.

Other ways to prevent heat illness include gradually building up workouts so the child can get used to exercising in warm weather. Adjust the practice schedule, activities and expectations to match the weather conditions, Rice said, and allow at least two hours of rest between practice sessions.

ORTHOPEDIC INJURIES

Causes: Sprains, strains, growth-plate fractures (damage to areas of cartilage near the ends of developing bones), tendinitis and other injuries to bones, ligaments and joints can be caused by falls, but also by overtraining in one sport, not stretching properly and not giving the body time to rest between workouts.

"Kids are getting more overspecialized at an earlier age," said Laurel Blakemore, head of orthopedics at Children's National Medical Center. She added: "Specializing in one sport at too young an age can lead to injuries, along with burnout."

Jon Almquist, who recently retired as the athletic training program coordinator for Fairfax County Public Schools in Virginia, agreed.

"Let the kid play sports to have fun playing sports instead of to boost the parent's ego," Almquist said. "Let them play different sports. Very few kids play sports to the point where they're going to be professional athletes."

Signs and symptoms: Swelling, limping, bruising and pain that is aggravated by activity are all possible signs of an injury. So is the inability to put weight on your knee or ankle.

Treatment: Most orthopedic injuries are treated successfully with rest, ice, compression, elevation, anti-inflammatory medication or physical therapy, Blakemore said. The child might have to wear a brace, boot or cast while the injury heals. Occasionally with a fracture or torn ligament, surgery is necessary.

Prevention: Proper training, including stretching, varying workouts and starting slow at the beginning of the season, is key to preventing many orthopedic injuries, Blakemore said.

Kayley Bogemann, 14, a sophomore at Centreville High School in Virginia, is working harder at prevention after a series of orthopedic injuries. Kayley plays club soccer and is on the cross-country and track teams at her school. She fell during a soccer game in 2011 and had reconstructive surgery on her ankle.

She also battled tendinitis and shin splints last year when she was going from running at cross-country practice to soccer, where she would run another few miles during conditioning exercises. Her mother, Beth Bogemann, said Kayley is trying to remember to stretch properly and to vary her workouts. When the rest of her team is running at soccer practice this fall, she will do footwork drills instead. And during cross-country season, her coach has her work out on an exercise bike one day a week instead of running, to give her knees a break.

"I've learned to be more careful with overworking my body," Kayley said.

For more information on sports injuiry clinics sponsored by Safe Kids Worldwide, go to safekids.org