The California Highway Patrol says it happened on Jefferson and Bethel just before 8 am.
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Officers say a Honda was heading east on Jefferson and drove through a stop sign.
The car was hit by an oncoming Chevy SUV driven by a 45-year-old woman on Bethel Avenue, which is not controlled by stop signs and has the right-of-way at the intersection.
Both cars veered off the roadway and into a vineyard after the collision.
A witness stopped and tried to help, but 27-year-old Adrian Gonzalez and his 4-year-old nephew, Enrique Flores Jr., died in the Honda.
Officers say Flores was not in a child restraint seat, booster seat or seat belt at the time of the crash.
Six other passengers in the Chevy were taken to the hospital.
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"You really have to use extra caution as you're traveling in these areas of the county," says Mike Salas with the CHP. "A lot of these intersections do not have four-way stops, so just be very vigilant as you approach these intersections."
The crash remains under investigation.
Drugs or alcohol were not factors in the crash.