According to police, several people helped the children escape from the locked trunk before 39-year-old Tori Castillo surfaced from the store.
Heidi, who wanted to keep her last name anonymous, was one of those people.
She told FOX40 sister station KSTU that she and her friend were unloading groceries nearby when she heard noise coming from the trunk. She walked over and put her ear against the car.
"I could hear some kids crying," she recounted. "I turned to my friend and I'm like, 'There's people in this trunk. There's kids in this trunk!'"
Heidi said she and her friend, as well as two other women, started trying to help the girl inside. She said one of the women had seen the mother put the children in the trunk, before walking into the store.
"I started talking to the little girl that I could hear screaming," Heidi said. "She was [yelling], 'Mom, let me out! Let me out! Mom! Help!' She was screaming, crying."
At that point, Heidi said she started yelling through the license place back at the girl, guiding her on how to open the truck with the emergency latch.
The trunk popped open. Heidi said the children were scared, and sweating from the heat.
"Both kids just came out...they just jumped out at us," Heidi said. "One lady took the 2-year-old, I took the 5-year-old."
While they waited for police, Heidi said the mother emerged from the store, according to KSTU.
"The only explanation she had was, 'My babysitter didn't show up,'" Heidi said.
According to the Riverdale Police Department, Tori Castillo was booked into the Weber County Correctional Facility in Ogden. She faces four counts of child abuse with physical injury, and one charge of theft.
The Division of Child and Family Services responded, "and the children were turned over to a responsible party," a press release stated.
Heidi still can't believe the shocking scene she witnessed.
"It was kind of heartbreaking to see that somebody could do something so cruel," she said