Arely Amaya, 18, is suspected of leaving her 1-year-old son and 2-week-old daughter in her car Saturday as temperatures reached 92 degrees outside, the Los Angeles Times reported.
Lt. Daniel Lopez of the East Los Angeles sheriff's station said it was about 10-15 degrees hotter inside the car than it was outside.
Deputies were alerted to the incident when a passerby noticed the children in the car, Lopez said.
"We really appreciate it when citizens call us with information like this," he said. "We'd like to thank that citizen who placed that call."
When deputies arrived, they were able to unlock the car and the children were kept in an air-conditioned patrol car until paramedics arrived, Lopez said.
Investigators said the children had been locked in the car for about 20 to 25 minutes.
Amaya was in custody Saturday night in lieu of $105,000 bail and faces possible felony charges for the incident.
The National Weather Service said dozens of children die every year from hyperthermia after being left in parked vehicles. Hyperthermia is an condition that occurs when the body takes in more heat than it can handle.
"No amount of time is safe to keep a child or pet in a vehicle when temperatures are this high," Lopez said.