A Dallas hospital is reminding parents how dangerous it is for children to be in a hot car by themselves.
Children's Medical Center has partnered up with the Safe Kids Texas Task Force to raise awareness about vehicular hyperthermia.
"Take action," said Johnny Humphreys, task force chair. "If you see an unattended child in a vehicle, that's a 911 call."
Last year, 4-year-old Lilly Parsons climbed inside her family's unlocked sport utility vehicle, became trapped inside and succumbed to the heat.
Her mother, Jodie Parsons, shared her story with other parents at Children's Medical Center.
"Until this happened to me, I really felt like it was something that I didn't have to worry about, and turns out that I very much did," she said.
The interior temperature of a car rapidly rises. NBC 5 observed how quickly a car heats up within 30 minutes.
Within three minutes, the thermometer read triple-digits temperatures. At the end of the half-hour, the final reading was 120 degrees.
And children's bodies heat up five times faster than adults, making them much more vulnerable to high temperatures.
"Children are very different," said Dr. Halim Hennes, director of pediatric emergency medicine at Children's Medical Center. "Children have a very large surface area. They also don't dissipate heat very well."
Last year, 33 children died of vehicular hyperthermia. So far this year, five children have died nationwide -- including one in Texas.