The mother of the children, a three-week-old infant and a two-year-old boy, was arrested for child endangerment.
The incident happened Saturday around 12:30 p.m. at the Mountain Grove shopping center, 27511 W. San Bernardino Ave.
Police got several calls about children locked inside a vehicle as the temperature outside hovered close to 100 degrees.
Police Cpl. Breanna Herrera responded and spoke with the children's mother, who said she had locked the keys in the car and they had only been inside for a few minutes. She said someone was on the way with a spare key and she didn't want the window broken.
But witnesses said the kids had been inside the car for at least 15 minutes. Herrera could see inside the vehicle that the children were not moving.
Herrera broke a window and entered the vehicle. She found the two-year-old boy seemed lethargic and in distress, while the infant was not moving.
The temperature inside the vehicle was determined to have reached 138 degrees.
She began giving medical attention to the children until paramedics arrived. Both children were brought to a local hospital and listed in stable condition.
Child Protective Services took custody of the children.
The mother, Danielle Marie Sulprizio, 26, of Loma Linda, was arrested for child endangerment.
City officials honored Herrera for her work rescuing the children and she is expected to be recognized at a future city council meeting.