As parents, youth sports officials and medical professionals struggle to find the safest methods for children to play football, public opinion remains mixed over when children should begin participating in tackle football and whether football is more dangerous than other contact sports.

Nearly six in 10 American adults, 57 percent, believe tackle football is safe for high school students, and slightly more than half, 53 percent, feel tackle football before high school is not a safe activity, according to a nationwide poll conducted in August by The Washington Post and the University of Massachusetts Lowell.

Asked what age is most appropriate to introduce tackling, 42 percent say it is appropriate for children to begin playing tackle football younger than age 14. Another 42 percent say children should wait until at least 14 years of age to start tackle football, with another 8 percent saying it is never appropriate.

Amid injury concerns, demographic changes, sport specialization and rising costs, football participation has struggled nationwide in recent years.

High school football enrollment is down 4.5 percent over the past decade, according to the National Federation of State High School Associations. Twenty-two states saw a drop in the number of high schools fielding varsity football teams over the past five years. Another 22 states added teams, or shifted some programs from 11-player football to six-, eight-, or nine-player football.

The falling participation coincides with broad public acknowledgment of the danger of head injuries, though professional football on television it remains as popular as ever.

The Post-UMass Lowell poll finds the vast majority of adults, 80 percent, say repeated brain traumas resulting in chronic traumatic encephalopathy, the neurodegenerative illness CTE, is "a serious public health concern."

Nearly the same proportion, 83 percent, consider the statement "playing football causes brain injuries" to be "settled science."

"It's probably not safe at any age. I think it's one of those things that I'm sure people get a lot of fun out of it and excitement, but for kids and adults I'm not really sure there is a safe way to do it," said Don Williams, 54, a pediatrician in Austin, Texas.

Medical professionals who study football, though, say children should begin playing tackle football at an age when they can fully adhere to coaches' instructions and properly wear safety equipment.

That's generally around age 8, said Ellen Smith, director of sports medicine at MedStar Montgomery Hospital and a practicing emergency room physician.

"The little guys can still generate quite a bit of force and a concussive level of force," she said, "but not enough force for the other kind of catastrophic injuries, like a broken pelvis or broken femur. It's important from a younger age to learn technique and discipline and all the things that make you a safer player when you're 16."

The poll finds youth tackle football is seen as safer among some demographic groups than others.

Hispanics and African Americans are more comfortable than whites introducing tackle football at earlier ages. About half of Hispanics and African Americans alike believe tackle football is safe before high school, while 38 percent of whites feel the same.

Men are more likely to say tackle football is safe before high school than women — 47 percent to 36 percent.

Those without college degrees are more likely to say tackle football is suitable for children before they reach high school — 46 percent of them say it's appropriate, compared with 31 percent of those with degrees.

Almost half of adults who have sustained a sports concussion, 49 percent, say football is safe before children reach high school — slightly higher than 41 percent among the public overall. They are also more likely to say football is safe for high schoolers (66 percent) than adults overall (57 percent).

Americans aresplit on whether heading a soccer ball is safe for children before reaching high school age, with 44 percent saying it is safe and the same share saying it is not.

Smith, the sports doctor, said heading a soccer ball is a skill children should begin to learn in their middle school years and use in games in high school. Players who do not have the proper training are just as likely to collide with another player and sustain a head injury as they are to successfully head the ball.

"That is a skill that is somewhat difficult for an 8 year-old," she said. "Heading in practice is different than heading in a game. It's one thing if your child is 8 and you take a non-wet, properly inflated soccer ball and throw it up to your child with a gentle toss. But it's a different thing to ask a child to do it in a game when you're running full speed and the ball is up in the air and you have to figure it out."

This Washington Post-UMass Lowell poll was conducted August 14-21 among a random national sample of 1,000 adults reached on cellular and landline phones. The margin of sampling error for overall results is plus or minus 3.7 percentage points.

Scott Clement contributed to this report.