ABC News' John Santucci, Santina Leuci and Rich McHugh report:
Chase Kowalski ran his first race when he was just two and a half years old. He won his first triathlon at 6.
Dylan Hockley was Chase's schoolmate at Sandy Hook Elementary in Newtown, Conn. Dylan was autistic, and his family had recently moved to Connecticut from England.
Both boys died Dec. 14, 2012, when Adam Lanza entered their school and fired on students and teachers alike, killing 20 first-graders and six educators before turning the gun on himself.
News of Son's Death Like a 'Physical' Blow
Ian Hockley, Dylan's father, described the moment he learned his child had been killed.
"On one level, there's what you're experiencing there, in the location, in the firehouse. And physically unable to move as this information's being thrown at you. And it's almost like physical blows," he said in an interview with Josh Elliott of "Good Morning America" that aired today on "GMA."
Rebecca Kowalski told Elliott she never thought she'd be able to recover from her son's loss, but something remarkable happened, just two days after the shooting.
She said Chase spoke to her in a vision.
"That … vision totally repaired my heart and just made it - I mean, it keeps us just going," she said.
In order to honor their son's memory and help other children experience his love for racing, Rebecca and Stephen Kowalski created a foundation in his memory and started Race4Chase, a grassroots funding campaign that encourages physical fitness.
Running as Therapy
The Kowalskis are gratified by the community's support of the organization.
"People just show up, you know," Rebecca Kowalski said. "They're present, they're here, and then they tell us, you know, 'I'm doing this for your son. I'm doing this because of your son.' It's beautiful," she said.
Ian Hockley, too, turned to running as therapy when chaos and heartbreak threatened to engulf his family.
"Putting one foot in front of the other is like getting up every day. We've got to get up every day for 365 days every year for however many years," he said.
He worked through his grief while he ran.
"So you get out on the road and it starts to get hard. And then just it hits you, It hits you while you're training," he said. "And when that wells up inside you, it chokes you up for a moment, and you almost feel like you have to stop. But then you punch through, and you go on, and you really know why you're doing it. And you can overcome anything then."
He and his wife, Nicole, now run along with members of Dylan's Wings of Change, the foundation they formed to raise awareness and funds for children with autism.
While Hockley uses running to work though his pain, he says, he hopes never to stop grieving because grief helps him remember his son.
To not do justice to Dylan's memory would be to leave his killing "a senseless act" and give in to negative energy, he added.
Parents Talk With Late Son
"So you've got to flip it around," he said. "Everything is about flipping emotions. Not hate, no hate. Flip it over. The other side is love, right? Take that and build, because once you push the hate out, the love just flows in."
Nearly a year has passed since their son's death, but Rebecca and Stephen Kowalski have kept his bedroom untouched, packed with all his toys and trophies.
The Kowalskis said they have conversations with Chase. She talks to her son mainly while she's in the shower, and he talks to him in the garage.
They both tell Chase how much they miss him.