CHICAGO (CBS) — Of the more than 2,000 COVID-19 deaths in Illinois, just three were under the age of 19. One of those was Caitlin Whisnant, who had just celebrated her 18th birthday.

CBS 2’s Jim Williams spoke with her family and explains why one group of children is particularly vulnerable.

Caitlin was the youngest of five children and loved to make other people happy, said her parents, Jody and Kristin.

“She was kind, quiet, loving, a wonderful child,” said Jody.

“Caitlin, she was my right hand here,” said Kristin. “If something needed to be done, she was always here helping me.”

“Even as a teenager she would hold my hand. She would my wife’s hand when we’d go out in public, and you know how rare that is. She didn’t care who knew how much she loved her family,” Jody said.

Caitlin, who excelled in math and science, was born with a genetic immune deficiency. Early this month she was diagnosed with COVID-19. She was then quarantined at her sister’s home. Her symptoms were not severe, her father says.

“I talked to her in a video call,” Jody said. “‘Honey, how are you feeling?’ ‘Dad, I feel fine. I’m just a little tired.'”

But minutes after that conversation, less than two weeks after her 18th birthday Caitlin died.

“I found her passed away and tried to revive her,” Kristin said.

The COVID-19 fatality rate among the young is low.

“Children compared to adults are a relatively less affected population when it comes to COVID-19,” said Doctor Larry Kociolek.

Kociolek is the director of Infection Prevention and Control at Lurie Children’s Hospital.

“About 80% of children that we have diagnosed withCOVID-19 have not required hospitalization, and many of those children have had such a mild illness that they probably did not need to be seen by the pediatrician either.”

Kociolek said physicians don’t have a full understanding why the mortality rate is so low among the very young, but he said many of those with difficulty have pre-existing conditions.

“I would want the world to know how wonderful our daughter was,” Jody said.

Caitlin’s parents are asking people to think of those who are the most vulnerable during this pandemic.

“You and I may feel fine, but this is about everyone else,” Jody said. “It’s about the bigger picture.”

Caitlin’s funeral was Saturday. Only family could attend. Her mother has COVID-19 and is recovering. No other family member has symptoms, they say.