Trejo, 75, was in the San Fernando Valley's Sylmar neighborhood when two vehicles collided, causing one to overturn onto its roof with a young boy strapped to a car seat inside, KABC reported.
The "Machete" actor crawled underneath the wreck but couldn't unbuckle the child's seat belt from his angle. Another bystander, a young woman, was able to get to the belt and Trejo was able to pull the child out, the news station said.
The boy's grandmother was trapped in the driver's seat and freed by firefighters with the Los Angeles Fire Department, the station reported.
The outlet said Trejo tried distracting the boy while fire personnel worked to free her.
"He was panicked," Trejo said of the boy. "I said 'OK, we have to use our superpowers.' So he screamed 'Superpowers!' and we started yelling 'Superpowers! I said, 'Do this, with the muscles.' He said 'muscles.'"
"We got kind of a bond. I kept facing him away from the accident," he added.
Fire officials said three people were taken to the hospital with non-life threatening injuries.
Investigators have not determined the cause of the collision.