"The last word she spoke was 'Mommy,' " Jen Petersen said. "And it haunts me to remember that."
The St. George couple shared their story Monday as part of a "Spot the Tot" campaign sponsored by Primary Children's Hospital in Salt Lake City.
The campaign urges drivers to take precautions when moving a vehicle, by walking a lap around cars to check for children, rolling down windows to listen while backing out or pulling forward, and eliminating distractions such as radio, phones and conversations.
Back-over injuries spike during the summer as people recreate outside, Primary Children's Hospital spokeswoman Jessica Strong said, and Utah averages one back-over incident every seven days.
"This is a tragedy for any family," Strong said.
Vehicle-safety features, such as cameras and obstacle sensors, are helpful, she said. But blind spots remain and areas of low visibility pose a greater risk to children.
"Human intervention is the best prevention," Strong said.
Jen Petersen said the accident was "excruciating." Family members began doing weekly service projects in memory of Natalie, Jen Petersen said, which led to their advocacy for vehicle safety and "Spot the Tot."
"No one is exempt from something like this happening," Jen Petersen said.
Chad Petersen said it's common to rely on a vehicle's safety features or to teach children to play out of the way of cars. But his truck was outfitted with cameras and sensors, and his children had received the same safety lessons as any other child, he said.
"Nothing replaces the human eye and being able to walk around that vehicle," he said. "It can truly make a lifetime of difference — just those few seconds."