"So I hope I can stop you from smoking before you miss out on life, too," Gabrielle says on the documentary. "And you go through what my mom has gone through. And you put your family and friends through this, too."
DeWitt said the documentary -- "Through My Children's Eyes" -- taught her that her children had "unbelievable hearts."
She's hoping that they will touch the hearts of other teens, and that the video will one day be played in every junior high and high school in Colorado.
Roughly four out of five people diagnosed with stage four lung cancer die within five years. More than half die within a year of diagnosis, and 75 percent die within two years.
DeWitt -- one of only 3 percent of lung cancer patients who got the disease under the age of 45 -- has defied the odds by surviving two years since diagnosis.
DeWitt is intimately aware of these statistics, but she said she did not have the courage to ask the doctor how long he thought she had to live. She told her family they could ask her anything except her survival rate.
Currently, DeWitt's cancer is "stable," and she says she wants to make the most of the time she has left.
Her children say the whole family is closer because of their mom's cancer, but they are brutally honest about the more negative effects of the disease on the documentary.
"They always say that the hardest thing for a parent to do is bury your child," Cody said on the documentary. "But the hardest thing for a kid to do is watch your parents die. Slowly. It's unbelievable and it's just horrible."
To contact the Susan L. DeWitt Foundation for Extended Breath, e-mail email@example.com.