"THEY KNOW the risks." That's the argument that is inevitably trotted out in any discussion about the dangers of playing football and the game's linkage to brain damage. Players, so this line of thinking goes, are willing to accept the risks in return for the game's benefits. That reasoning, while perhaps acceptable for adults, flies out the window when it comes to children. Children aren't allowed to accept the risks of smoking cigarettes or drinking alcohol, so it defies logic to let them accept the dangers that football may present to their developing brains.

A picture of these dangers emerged from a long-term study published last week by Boston University researchers who examined through phone interviews and online surveys a sample of 214 former high school, college and professional football players. Those who started playing contact football before the age of 12 suffered more behavioral, cognitive and emotional problems than those who started playing after they turned 12. Exposure to repetitive head impacts may double the chances of developing behavioral problems and triple the risk of experiencing depression.

"The brain is going through this incredible time of growth between the years of 10 and 12, and if you subject that developing brain to repetitive head impacts, it may cause problems later in life," said Robert Stern, one of the authors of the study from the university's Chronic Traumatic Encephalopathy Center. The study made no policy or rule-change recommendations for youth tackle football, citing the need for further study. But Mr. Stern told the Boston Globe, "I'm at a point where I feel comfortable saying that, based on logic and common sense and the growing totality of the research, I don't think kids should be playing tackle football."

Apparently, he is not alone. Participation in youth tackle football has fallen off, and, as the New York Times reported, schools across the country have ended programs "because of safety concerns," with parents switching their children to other sports . Youth football leagues have instituted practice and rules changes in a bid to make the game safer, but this report — along with the Boston University center's earlier study that found 110 out of 111 brains of deceased NFL players had degenerative brain disease — should give pause to any parent who thinks playing football would be in their child's best interest. Yes, there is some risk in most sports, but the emerging evidence seems to put football in a category of its own.