(NEW YORK) — Crystal and Brian Clark are on a mission to save lives after their children were struck and killed by a falling tree during a family camping trip last year.

The Clarks started a billboard campaign to honor their children, 9-year-old Xander and 8-year-old Ziva, who they described as “very loving” and “kindhearted,” and shine a light on the hidden dangers of falling trees.

Their sign includes a photo of Xander and another photo of his sister Ziva, alongside a message that reads: “Check your trees! After storms, heavy rains and windy days. You could save a life! Xander and Ziva Clark killed by a fallen tree 4/23/22.”

“My whole thought of a billboard came a few months after the kids had passed, to where I can share who they were and how great of kids they were, but also spread awareness of something that isn’t ever thought of really by a parent until it actually affects you or a family member,” Crystal Clark told ABC News’ Good Morning America.

“You expect your child to fall out of a tree, not a tree to fall on them,” Brian Clark added. “But apparently, deaths by tree are not as uncommon as we all thought. So to me, that’s why it is important to get the word out.”

The Clarks had gone for a golf cart ride on April 23, 2022, a day Crystal Clark remembered as a sunny one but also marked by strong winds. She said they were driving under a “canopy of trees” at a Cloverdale, Indiana, campground when the unthinkable happened.

“We heard a very loud noise, almost sounded like a plane crashing into the woods,” Crystal Clark said. “Next thing we know, the tree had fallen. It was too late for us to notice it and I shouted, ‘Our babies!’ and Brian and I got off the golf cart and that’s where we saw that they were gone.”

“It was just a sight that you hoped you never had to see,” Brian Clark added.

In the months since their children’s unexpected deaths, the Clarks said they started hearing from other people with similar heartbreaks.

“After we went through our incident with the children, we realized it was more frequent than anybody really ever talked about,” Brian Clark said. “The more we heard from people, the more people that reached out and said, ‘We know what you’re going through."”

Last Sunday, a mother hiking with her son and his Boy Scout troop in Cupertino, California died after a tree fell on her.

The U.S. Forest Service notes that trees can fall at any time, without warning, and warns people to be alert for trees on windy days or after an ice storm or snowstorm. The agency also said trees with “structural defects” can have a lack of needles, bark or limbs and those with internal rot may have “conks, broken tops, basal scars, numerous downed limbs, ants, or an abundance of woodpecker holes.”

“Look up while on trails, especially when it’s windy,” the Forest Service advises. “Stay out of the forest when there are strong winds that could blow down trees. If you are already in the forest when winds kick up, head to a clearing out of reach of any potential falling trees.”

After hearing of the Clark family’s motivation to turn their heartbreaking tragedy into purposeful action, Lamar Advertising Company decided to sponsor nine additional digital billboards in the central Indiana area, along Interstate 70.

“The digital billboards actually went up last Thursday. It was kind of nice because that was my husband’s birthday. So that was a nice surprise for us,” Crystal Clark said.

Brian Clark said they “greatly appreciate” the company’s support and generosity and hope their important message can help others.

“If you save one more life, that to me, is a good thing,” he said.

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