Games should start with a warm-up to avoid damage to “cold” tissues. Adequate rest beforehand is always important — tired players don’t think clearly or play well — and good hydration is essential throughout the game.

I should also mention the importance of good nutrition. Children who are deficient in vitamin D, for example, are 3.7 times more likely than those with normal levels of the vitamin to sustain a fracture that requires operative repair, Dr. Pooya Hosseinzadeh, pediatric orthopedist at Washington University, reported at a recent meeting of orthopedic surgeons. In her study of 100 youngsters with forearm fractures resulting from low impact (like falling from a standing height), 49 percent were vitamin D deficient and half of those required surgery.

In an interview, Dr. Hosseinzadeh said, “Children are not getting out into the sunshine enough nowadays, and they’re not consuming enough seafood and fortified milk,” the main dietary sources of vitamin D. When vitamin D levels are low, calcium absorption is impaired and the body takes the mineral from one’s bones to maintain a proper blood level. “The bones get weaker and break more easily,” she said.

Dr. Elizabeth Matzkin, orthopedic surgeon and chief of Women’s Sports Medicine at Brigham and Women’s Hospital, also emphasized the importance of eating enough. “Energy going in should be adequate for the amount going out,” she said, “If not, bone health can suffer and bone stress injuries can result. You can only build one’s bone bank to age 25. We don’t want kids starting out with too little in the bank.”

Probably the most common injuries among young athletes result from overuse, which causes undue stress on certain body parts, like the tissues in a Little Leaguer’s elbow. Overuse injuries result when a child continually uses the same muscle groups and applies the same stresses to a specific body part, resulting in muscle imbalances and inadequate time for repair. Common overuse injuries include shin splints and Achilles tendinitis.

To avoid such injuries, Dr. Matzkin recommends “diversification — playing multiple sports and different positions so they’re not doing the same motions with their bodies over and over again.” She and other experts recommend that children under the age of 16 not practice a given sport for more hours a week than their age in years. Children who play the same sport on more than one team in a given season are at increased risk for injury. Likewise for those who play and train for the same sport all year, with no downtime to allow overstressed tissues to recover and without other activities that feature different parts of the body.

Participating in different sports helps youngsters develop “good biomechanics,” which reduces injury risk, Dr. Matzkin said.