Whether it's little tykes in oversized pads or high school kids in serious competition, the dangers of high-impact sports are in the spotlight. Coaches and parents are aware they need to keep their athletes' heads protected to avoid the dangers of concussions.

Researchers from University of California at Berkeley, Duke University and the University of North Carolina at Chapel Hill say even children who play a single season of football can experience microscopic changes in their brains. The team analyzed MRIs of players between the ages of 15 and 17 after football season and discovered changes in the gray matter in the front and back areas of the brain.

"It is becoming pretty clear that repetitive impacts to the head, even over a short period of time, can cause changes in the brain," said study senior author Chunlei Liu, a member of the Helen Wills Neuroscience Institute at UC Berkeley. "This is the period when the brain is still developing, when it is not mature yet, so there are many critical biological processes going on, and it is unknown how these changes that we observe can affect how the brain matures and develops."

While the study didn't focus on the consequences of repeated hits to the head, the researchers did caution on how often children should play sports.

What about completing banning high-impact sports for kids?

Bob Costas and Dr. Bennet Omalu, Concussion Bob Costas (left) and Dr. Bennet Omalu attend the New York premiere of "Concussion," a movie that told Omalu's story and his efforts to study and publicize CTE in the face of NFL opposition. (Photo: Dimitrios Kambouris/Getty Images)

Dr. Bennet Omalu, the forensic pathologist who was the first to discover chronic traumatic encephalopathy (CTE) in the brains of former football players, has a more extreme idea. He warns that children who play contact sports could face a lifetime of serious health problems and details his concerns in his book, "Truth Doesn't Have a Side: My Alarming Discovery about the Danger of Contact Sports."

Omalu, whose story was depicted in the movie "Concussion," suggests that children should never play sports like football, hockey, rugby and even lacrosse.

"Knowing what we know today, there is no reason whatsoever that any child under the age of 18 should play the high-impact, high-contact sports," he told Today.

"The big six are: American football, ice hockey, mixed martial arts, boxing, wrestling and rugby. Blows to the head are intrinsic to the game. That truth could be inconvenient, painful and difficult, but we should not deny it."

Omalu says letting a child play football is the "definition of child abuse."

"We wouldn’t give a child a cigarette to smoke because a cigarette is potentially harmful," he says. "But we would put on a helmet on the head of a child and send him out on a field to play a game whereby he sustains repeated blows to his head, to suffer sub-concussions and concussions."

Instead, Omalu suggests safer sports such as swimming, track and field, volleyball and basketball.

Editor's note: This article has been updated since it was originally published in September 2017.

Mary Jo DiLonardo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.

Why kids shouldn't play football until they're 18
The doctor who discovered the dangers of concussions says kids should avoid high-impact sports until they are 18.