Ten years after Sandy Hook: 'It is who I am'

STORY: "Time is a curious thing. Sometimes I feel like it was yesterday, sometimes it's, I guess quite, literally a lifetime ago."

Marc Barden's son, Daniel, was a student at Sandy Hook Elementary - a seven-year old with an outsized sense of empathy.

"We used to kind of jokingly call him 'the caretaker of all living things,' because he would literally stop and pick up the worms off the sidewalk and put them in the grass so they wouldn't burn in the sun. Or he would carry the big carpenter ants out of our kitchen, because he thought, he thought they should be outside with their families.

But on December 14th, 2012, a heavily armed man burst into his classroom in Newtown, Connecticut, and started shooting.

MEDICAL EXAMINER (2012) "this probably is the worst I have seen or the worst that I know of any of my colleagues having seen..."

RINEI HAWKE:"We always thought it was going to be us next. When the round of shooting stops, it's like, oh, it's going to be us next."

Nicole Rinei Hawke, now 17, remembers back ten years ago, hiding in her second-grade classroom.

RINEI HAWKE "After what felt like hours, we had... we had people knocking on the door, saying that it was them. And then we started getting let out, told us to close our eyes, which thankfully I did. I know some people who didn't and now they have to suffer with that image in their minds. But luckily I kept my eyes closed, and we walked out there safely."

As word spread, parents rushed to the firehouse to pick up their children.

BARDEN: "And the line at the first grade and all the grades kept getting smaller and smaller. And most of the people were gone. And I was like, 'Where's Daniel's class?' Like, I couldn't, I don't know why Daniel's class hasn't come out yet."

Nicole Hockley recalls searching for her son - Dylan.

HOCKLEY: "And I said, 'Where's the rest of the class?' And they said, 'I don't know.' And I looked down at the children that were there, and I recognized Dylan's reading partner, a beautiful, intelligent girl. And her eyes were just... she was just staring, and, and I just backed away. // And people started saying, 'tell us what's happening.' // He said, 'If you are still waiting here, then the person you're waiting for isn't coming back.' And the room just erupted in chaos."

BARDEN "and that's where they announced that, you know, there was this horrific mass shooting. And that's... that's where we learned... that's where we learned that Daniel had been shot to death, hiding in a closet in his first grade classroom."

In the end, 20 first-graders and six adults were dead.

In the decade since 20-year old gunman Adam Lanza's rampage, debates have ignited in the United States over mental health, access to guns and how best to secure schools.

For the people closest to the horror, marking this moment is mixed with anger, profound loss, and still, some hope for change.

The murder of their children drove Barden and Hockley into advocacy, working to try to save other children from the same fate.

BARDEN: "For me, I feel like it's a very appropriate way to honor Daniel because I've always thought he was going to do such wonderful things in this world with that beautifully, naturally developed sense of compassion and awareness of others. And it was taken from him. And I feel a very real sense of responsibility to try to fill those enormous shoes in whatever way I can.

HOCKLEY: "I had talked at Dylan's funeral on the 21st of December about... about that change needed to come from this. And I said at his service, I didn't know what that change was, but I felt that, you know, we couldn't have just lost our son and had 26 people killed and nothing come from it.

Barden and Hockley started a nonprofit organization called Sandy Hook Promise.

The group aims to educate students, teachers and others about the warning signs that could help identify potential mass shooters, and ensure authorities are alerted when such signs are seen.

More than 18 million people have participated in the group's programs. The group says at least 11 school shooting plots have been foiled in recent years because of the training.

HOCKLEY: "It's very hard for me to think about the fact that it's been ten years since Dylan was killed, because and, you know, it's also just like a blink of an eye. And I could still look in the rearview mirror and expect to see him sitting in his carseat in the backseat. But I have never lost hope in people and our ability to do the right thing. // So I wish now that, you know, having been ten years later that no more school shootings were happening and that gun violence was a thing of the past. It's probably going to take more than another ten years to get there. But as long as we have the will, we'll just keep moving forward."

RINEI HAWKE: ""It's not something that changed me. It's something that is who I am. Ten years after, it's actually becoming more frequent than less, so it's definitely made me an angry or person, politically, at least. And I think that I care a lot, because of it, I care a lot more about things that normal high schoolers shouldn't."