The crash happened around 8 a.m. as the woman, who is about 30 years old, and her son walked through the parking lot of Green Acres Elementary School at 966 Bostwick Lane, CHP Officer Jason Morgan said.
A female driver, also about 30 years old, was about to pull into a parking spot in the lot when she accidentally hit the gas pedal instead of the brake and accelerated into a nearby chain-link fence, Morgan said.
The end post of the fence became dislodged and struck the female pedestrian in the head, causing major injuries, Morgan said. The 4-year-old boy sustained minor injuries, he said.
Both victims were airlifted to a trauma center, Morgan said.
The driver, who had a toddler in her car, is not suspected of being under the influence of drugs or alcohol and was not arrested, Morgan said. The toddler was uninjured in the crash.