New York ? Enthusiasm and energy are among children’s best attributes. Given the chance, they’ll run, jump and play at the drop of a hat.

Unfortunately, though, rushing into a game of soccer or turning cartwheels without stretching first could be harmful to their able-yet-vulnerable bodies.

Even worse is when children take time off from physical activity, particularly during summer and holiday breaks, and then return to the gym or field expecting to pick up exactly where they left off, says Peter Kormann, gymnastics director of Chelsea Piers, a New York City sports complex.

“We call the week after summer vacation the worst week of the year because it’s the greatest chance of injury,” according to Kormann, who coaches everyone from 17-month-old toddlers to senior citizens. Most of his gymnasts are between 5 and 13 years old.

“Kids don’t realize they need a long warmup and gradually get back into shape and retrain their muscles.”

In a high motion sport, such as gymnastics, basketball or football, young athletes can take about a week off without really risking injury upon their return, Kormann explains. If they take more than a week off, they should be careful for the first few days of physical activity, and extra careful if they’ve been off for two weeks. Beyond that, kids will need to recondition and shouldn’t play anything competitively until they’ve worked their strength back up, he advises.

“I try to teach kids that part of being an athlete is training and conditioning,” says Kormann, a former Olympian, and Olympic and college coach.

One problem with organized youth sports from a medical point of view is that there isn’t a registry to track ages and other commonalities among injuries, says Dr. Mary Lloyd Ireland, president of Kentucky Sports Medicine in Lexington, Ky., and the medical director of the Women’s United Soccer Association.

She urges parents and coaches involved in these leagues to talk to local doctors about the risks of various sports and the prevention of injury.

One way to avoid injury is learning to do things the right way, Ireland says, including how to properly “head” a ball in soccer and how to land after leaping.

An abrupt action, such as running, stopping and quickly changing direction, can be awkward as the brain and body are trying to do too much at once, she explains. The best preparation for this is practicing it repeatedly in a controlled environment.

Like adults, children need to get in shape to get in shape, Jan Griscom says. She’s a personal trainer at Chelsea Piers and served on the faculty advisory board of the American Council for Exercise.

She suggests children who are beginning a fitness routine start with slow-control movements, such as abdomen crunches or back extensions, and work on their balance, which can be done simply by standing on one foot.

Of course these beneficial movements aren’t as much fun as kicking a goal or tumbling on the ground so it’s important for parents, coaches and trainers to make warming up fun, Griscom says. “Being physically active doesn’t always mean ‘sport,’ it could be any movement, including play with a purpose.”

Some options include marching, jumping rope, playing tag and riding bikes. One of the most effective lessons in balance and control, according to Griscom, is to sit on an oversized exercise ball, such as a Physioball, and throw a smaller ball back and forth to someone sitting on another exercise ball. A warmup doesn’t have to add a lot of time or expense to an overall exercise routine, she adds.

“I’ve never seen a 4-year-old that wasn’t smiling or laughing when they were running unless he was being chased by a dog,” Griscom says.