Kato was walking back toward the check-in line where Gail and the children were standing with the luggage when it happened: ISIS suicide attackers detonated two suitcase bombs.
Thirty-five people were killed and 300 wounded. Like so many others', the Martinezes' lives were devastatingly altered in the space of seconds.
The Martinez family wants the world to know what ISIS took from them that day, and talked exclusively to CNN to share their experience.
Gail Martinez -- Kato's wife -- was killed. Their four children suffered serious burns, shrapnel and broken bones in the blast. Now Kato, clearly very much still grieving, is raising all of the kids on his own.
"For the longest time, I was sad, I was depressed, I was frustrated, because one of the things my wife and I had promised each other -- really I promised her, because it was expected I would go first -- but we promised each other, should any one of us go before the other, that we would haunt each other," he recalled.
"For the longest time afterwards, I was depressed because I didn't see her. I didn't see her. She wasn't haunting me. She broke her promise," Martinez said.
But recently things have changed.
"As time went by," he noted, "I looked back (on) all the things that's happened to us. I see her in the faces of my children. I see her in this house. I see her in the people that come to help us. I see her in all the things that have been done for us, to support us, to help us, all the good things that have happened."
The oldest, 18-year-old Kianni, is unflinching. She wants the world to know Gail was everything to the family: "I live every day because of her. I live every day for her. And to remember her. And to honor her."
Kianni is still dealing with the aftermath of yet another surgery on her injured leg. She was supposed to start college this fall on a ROTC scholarship, but with her injuries, she still has to pass the physical fitness test required to receive her ROTC scholarship --something she is determined to do.
"I'm pushing through it, every day. It's difficult to go through the pain. But you have to look forward," Kianni said.
"I think it's important for me to talk about this, because right now you hear adults talking about it, you see it on the news, but at 18, you're supposed to be going to college, becoming independent, having been prepared for everything by your parents, and then trying to learn for yourself what the real world is like," she explained. "The real world slapped me in the face on March 22. And I'm not going to forget that."
Kato, 48, himself was grievously hurt in the attack. Initially he was not even able to leave his bed in the Belgian hospital to see his children.
"My left leg was third-degree burned. My left foot was almost severed," he recounted. "I had a bullet wound in my calf. Left ankle, left heel was fractured due to a penetration wound coming laterally from the left. I had shrapnel wounds in my right foot, shrapnel wounds in my back, second-degree, third-degree burns on my scalp. My right hand was almost severed."
He recalled the moments after the blast: "I knew I was bleeding out and my body was going into shock, so I closed my eyes and welcomed it and figured I'd join my wife" and children.
"As I was slipping away, I heard this little girl call out to me, 'Daddy, don't you go. Don't you leave me,' " he continued, his voice breaking. "Just when I thought I was enveloped by darkness and ready to go to sleep, I heard her voice and decided to come back."
Kato said his first instinct in the seconds after the blast was to look for his family -- even as he was bleeding and hurt.
"I later learned I took most of the shrapnel, if not all the shrapnel, because my son took the secondary wave, and he got the burn, the flame. I didn't lose consciousness. I was blasted forward, and I knew I was bleeding because I felt blood coming from ear. Apparently my head was on fire."
But he couldn't locate them.
"I couldn't find my son or my two youngest," he said. "I heard screaming and I found Kianni. The fact that she was screaming, I knew that she was alive, she was coherent. I went to look for her mom. I said, 'I'll be right back.' I went to look for her mom."
But Gail was dead.
"The story I got from one of the first responders regarding my baby, the youngest one, was that they found her in Gail's arms," he related. "This is a testament to Gail's strength and what a mother would do in a last possible moment. She protected Kailani and held her until help arrived.
"The first responder proceeded to tell me that when they got to her, they told her, 'We got the baby now. She's going to be okay.' That's when she looked up to them, smiled and closed her eyes for the last time."
Kailani was seven years old and badly burned.
Kato's military buddies, who were stationed nearby, and their families came to help him in the hospital -- staying with the children in their hospital rooms, making sure they were never alone, going back and forth to Kato's room to tell him about their medical care and progress.
"They did shifts around the clock, making sure that my children were taken care of and there was always a friendly face there," he said.
Now they are home in Texas, trying to move forward. Kailani and her nine-year-old sister Noelani love to put on aprons and help Kato cook meals in the kitchen.
Thirteen-year-old Kimo suffered third-degree burns on his lower body. He is in physical therapy to loosen the scar tissue, and he wants very much to play sports again. He has his eyes set on going to MIT one day to study mechanical engineering to design the next generation of sports cars.
And Kianni is determined to get her strength back and attend college on that ROTC scholarship.
No easy college courses for her, she said that she plans to study "artificial intelligence and robotics" -- and make the military her career.