The single-car crash happened around 1:30 a.m. on the northbound Sagtikos Parkway, just south of Exit S3, in Brentwood.
Authorities say 31-year-old Carlos Martinez was driving a 2005 Dodge Caravan when his vehicle began to exit the roadway and mount the right shoulder. He then crossed both northbound lanes of travel and entered the center median before striking the guardrail.
The vehicle subsequently rolled over in the roadway and onto the child, who had been ejected during the accident.
Two passersby witnessed the accident and stopped at the scene, and they were able to pull the child from under the vehicle.
Martinez was also ejected and was pronounced dead at the scene.
The child was transported to Good Samaritan Hospital with serious injuries but is expected to survive.