SACRAMENTO — California lawmakers will debate on Wednesday whether to ban tackle football for children below the age of 12, a move pushed by advocates seeking to protect tots from brain damage but opposed by coaches who warn it would cut off youths from an important source of physical activity.

The bill, authored by a Democratic assembly member, Kevin McCarty, is scheduled to have its first public hearing before a legislative committee and is still a long way from passing. Wednesday’s hearing is crucial; the bill must clear the state Assembly by the end of January to have a chance of becoming law this year.

If passed, the bill would not take effect until 2026. Proposed amendments would gradually phase in implementation through 2029. The bill comes as flag football has been gaining popularity nationwide, especially for girls.

Research has shown tackle football causes brain damage, and the risk increases the longer people play football, said the chief executive of the Concussion Legacy Foundation, Chris Nowinski, a former Harvard football player and WWE professional wrestler. It can cause chronic traumatic encephalopathy, which causes the death of nerve cells in the brain.

“I don’t have a problem with NFL players, who are adults and understand the risk and are compensated, risking CTE,” Mr. Nowinski said. “I can’t imagine a world in which we have children, who don’t understand the risk, doing this for fun (and) taking the same risk with their brain.”

No state has banned tackle football for children, but there have been attempts to do so. Similar bills that were introduced previously in California, New York and Illinois failed to pass.

California law already bans full-contact practices for high school and youth football teams during the offseason and limits them to two practices per week during the preseason and regular season. A law that took effect in 2021 also requires youth football officials complete concussion and head injury education in addition to other safeguards.

A former youth football coach, Steve Famiano, who leads the Save Youth Football California coalition, said youth football leagues need more time to implement the 2021 law to see how effective it is. He said tots under 12 shouldn’t be forced to play only flag football, which he said is a completely different sport from tackle football.

“Flag football is oriented toward leaner, faster kids, and some of the kids we see in tackle football may not have developed yet physically, they may be a little bit overweight or are larger in stature, maybe not the fastest kid on the team,” he said. “They fit so perfect on a youth football team. They get to play offensive line and defensive line. You take that away from those kids, where do they go?”

Tackle football at the high school level has been declining in California. Participation dropped more than 18 percent between 2015 and 2022, falling from a high of 103,725 players to 84,626 players, according to the California Interscholastic Federation’s participation survey. Football participation increased by 5 percent in 2023, up to 89,178 players.