The parents of a young Indiana girl killed by a freak sand hole collapse at the beach are recounting the moment their daughter was swallowed alive.

The Mattinglys were vacationing in Lauderdale-by-the-Sea, Florida, with their two kids when tragedy struck Feb. 20.

"We were just relaxing," Jason Mattingly explained during an exclusive interview with Good Morning America from his family's home in Fort Wayne, Indiana, that aired Thursday. "We were just getting ready to end our day there. And then that's when the incident happened."

Jason and Therese Mattingly's 7-year-old daughter, Sloan, and 9-year-old son, Maddox, were digging a hole in the sand, when it collapsed and both children became buried.

"It just became chaos and horror," Therese remembered, adding that it all happened "really fast."

The parents, along with several onlookers, immediately sprang into action to desperately try to dig the children out as fast as they could.

Maddox - who was buried up to his chest - was pulled out first, and escaped without injury, his family said. But, Sloan was trapped completely beneath the sand for nearly 15 minutes.

"That part just hurts really bad because it didn't matter that we were literally right there," she said. "It was just a hole, and then there's nothing."

"Everyone tried their hardest," Jason said of the beachgoers' efforts to help them reach their daughter. "And unfortunately, it didn't work out in our favor."

Sloan was pulled out by firefighters and pronounced dead on the scene.

"It's kind of a blur, and it's probably my mind protecting itself, but it just happened so fast," he said. "And in my mind I had her in my hands, but the weight of the sand was too much."

The family returned to Fort Wayne and laid the first-grader to rest March 1.

Now, they're reflecting on the time they shared with Sloan in those short seven years, and figuring out how to navigate life as a family of three. They're also looking to the future in hopes of channeling their grief into action.

"I don't know what steps to take in order for that to happen - for, you know, signage or lifeguards or patrol," Therese said. "But hopefully we can make some sort of change from this."