The California Highway Patrol identified Mario Lopez-Alaniz, 25, and Angel Granados, 7, as the two victims killed in the crash.
The driver, 41-year-old Ana Trujillo, is believed to be Lopez-Alaniz's girlfriend and Granados' mother. She was driving a 2003 Isuzu eastbound on the 91 Freeway near Harbor Boulevard at about 12:40 a.m. with Alaniz in the passenger seat and Granados in the back.
According to the California Highway Patrol, the couple got into an argument. For unknown reasons, Alaniz interfered and grabbed the wheel, the California Highway Patrol said. The woman lost control and the car veered off the freeway and into a dirt embankment before colliding with a tree.
Authorities say the female driver was not drunk, but they have not ruled out the passenger may have been intoxicated.
Lopez-Alaniz died at the scene, the California Highway Patrol said. Officials with the Anaheim Fire Department said it took some time to rescue the boy from the SUV because of how badly mangled the car was.
The boy and mother were hospitalized at UCI Medical Center, where the child later died. The woman suffered minor injuries. Authorities say she is fully cooperating.
The California Highway Patrol is looking for witnesses in the case.
According to court records Lopez-Alaniz was on probation after pleading guilty to the sale or transport of a controlled substance last July. Three months before that, he pleaded guilty to driving without a valid driver's license.
Police are investigating to see if drugs or alcohol played a part in his decision to allegedly grab the steering wheel that led to the fatal crash.
CORRECTION: It was earlier reported that Alaniz was the child's father. It was later clarified that the two were not related. The boy's age has also been corrected from 6 to 7.