From what he remembers, and it isn't much, Cameron Williams was cold.

On a steaming autumn day last year in Burtonsville, the 13-year-old shivered as he walked back to his Unity Thunder football team's huddle, barely able to keep his eyes open. Dizzy, he'd been hit hard —really hard —twice that game.

His head ached for relief, but he knew how football players were supposed to act. How pain was a part of the game. Then he took two more vicious hits at practice the next day, and Cameron realized it was time to tell someone how much he was hurting.

His mother whisked him away to the family doctor, who told Cameron he'd been concussed twice in the past week.

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Because of the undeveloped nature of their bodies, youth like Cameron could be at a higher risk for concussions than their professional counterparts, according to medical experts.

But of the estimated 4.5 million children who play organized youth football in the United States, his experiences aren't altogether uncommon. A 2006 study by the National Center for Injury Prevention found that 47 percent of high school football players sustain a concussion each season, and 35 percent of players said they had more than one in the same season.

As concerns regarding head safety in professional football continue to mount, a sea change at the sport's most formative level has taken hold. Thirty-five states, including Maryland and Washington, D.C., have enacted laws that formally strengthen the treatment and prevention of concussions in youth sports.

Cases such as Williams' have opened the eyes of administrators of the game. His league has adopted changes to make sure coaches are trained in first aid, including concussions.

Walter Moyer, Cameron's coach, said the league now screens parents before selecting teams to identify nurses and doctors. Those parents are spread across different teams to ensure medical help is available at every game.

"We only know so much as a coaching staff on what to do with treatment and such, so we need (that) extra help on hand," Moyer said. "The problem comes when the kid is a star kid and he has that desire to get back out there and a coach who may not be as well versed in the injury, and the coach tries to look out for the best interests of the team and the game instead of the kid."

Those worries have spread to parents as well.

"My feeling is that I'm entrusting my child into your care," said Clennie Murphy, a parent of two youth football players in Silver Spring. "You want to have somebody to have the best interests of your child."

While concussions in college football and the NFL have garnered more of the spotlight, medical experts said more focus is needed on injuries at lower levels.

"We know that our youth are at a greater risk for head injuries," said Dr. Robert Cantu, a co-director of the Center for the Study of Traumatic Encephalopathy at Boston University and one of the field's foremost critics of collision sports in youth. "I think the risk-reward is just not there."

In February, the NFL announced it was urging all 50 states and the district to pass legislation that could help limit concussions among young football players.

The timing of the league's message was not random. The week before, former Chicago Bears defensive back Dave Duerson fatally shot himself in the heart at age 50 after a prolonged battle with depression stemming from a case of chronic traumatic encephalopathy.

CTE, a progressive degenerative brain disease normally associated with repeated blows to the head, had long been linked to boxers. It has now been connected to more than two dozen deceased former professional football players. Last year, an autopsy showed the disease was present in the brain of a 21-year-old University of Pennsylvania football player who hanged himself after having never been diagnosed with a concussion.

"Now that the public is more aware, we have a lot less problems on an individual basis within our own system," said Jon Almquist, the athletic training program administrator for Fairfax County Public Schools. "We used to have to fight tooth and nail and argue with the parents."

The more parents and coaches know, the better, Cantu said. His research at Boston University has shown that despite their small size and low speeds, youth are more at risk for head injuries than their professional idols.

Their vulnerabilities, Cantu explained, stem from their still-growing bodies and brains. With disproportionately large heads and relatively weaker necks, young players offer an easier target than a filled-out adult. The neurons in their growing brains have not been fully protected with myelin, a fatty substance that insulates nerve cells.