In a video shared by the outlet, the 75-year-old explained to authorities on the scene he witnessed a lady run a red light and crash into another vehicle, which caused it to flip over on its roof.
The Los Angeles Fire Department disclosed to CNN partner KABC that three individuals were taken to a medical clinic.
But some of the victims had been trapped, said L.A. Police Officer Tony Im.
Trejo says another bystander, a young woman named Monica Jackson, was able to undo the buckle. After Jackson unfastened the auto seat's buckle, Trejo was able to pull the youngster - a special-needs child - out of the vehicle.
Together the pair pulled the baby safely from the wreckage.
There was no information available on the victims' conditions, both Stewart and Im said. "My baby!", and Trejo, along with another bystander, got to work saving the child, who was still in his vehicle seat.
"God bless you, pay attention", he said. "We got kind of, like, a bond, I guess". "I kept facing him away from what was going on".
Trejo stayed with the boy after he was freed until his grandmother was pulled to safety by rescue workers.
The Machete actor said he tried to distract the little boy from looking at the accident.
"And the only thing that saved that little kid was his vehicle seat, honest to God".
"Everything good that has happened to me has happened as a direct result of helping someone else".
Trejo has been acting since 1985 and has appeared in hundreds of roles.
In addition to credits in such films as "Heat, ' "Con Air" and "Desperado, ' he is perhaps most recognised as the character Machete in the 'Spy Kids" movies and later in his own 'Machete" action film and its sequel, 'Machete Kills'.