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Harrison Fields was only five years old when his mother, an NYPD detective serving in the Medical Examiner’s office, responded to the 9/11 terrorist attacks on America, an event that has left him and many others with a "feeling of fear" 20 years later.

"On that blue-sky morning, I remember St. Joseph's Catholic School going on lockdown and there being an immediate concern in the air. My teacher rolled a TV into the classroom, and before my eyes were two familiar structures on fire," Fields recalled in an opinion piece for Fox News.

While at the time he was "confused" about the situation, Fields said the "confusion soon turned into worry as I remembered that my mom worked near those smoking buildings."

Fields later recalled that his grandfather, a retired NYPD Sergeant, picked him and his siblings up from his school. "My grandmother was noticeably on edge, the phone rang non-stop, and my mom was nowhere to be seen or heard," he said. "Morning turned into afternoon, and still no sign of my mom—just the cold feeling of worry and fear."

HARRISON FIELDS: ON 9/11, I WAS 5 YEARS OLD AND SON OF AN NYPD DETECTIVE. I WONDERED, 'IS MOMMY ALIVE?'

"The towers collapsing, the Pentagon attack, and the crash in Shanksville, Pa., doesn't serve my memory well but the towers billowing smoke and the feeling of fear will forever rest uneasy in my psyche," Fields said, noting that as the hours drifted on he "went to bed unsure if my mom was dead or alive."

Shortly after midnight on September 12, 2001, Fields found out that his mother had survived, however she was unsure of when she would be returning home.

"I will never forget the feeling of knowing that my mommy was alive and OK," Fields said.

Unlike Fields' situation, several children never heard the voices of their mothers or fathers again.

Jackie Hobbs, now 32-years-old, lost her father in the 9/11 attacks on America and spoke with the New York Post about life after and working as an associate media director at an ad agency whose headquarters overlooks Ground Zero.

As noted by the Post, Hobbs' father, Thomas Hobbs, 41, worked on the building’s 105th floor as a broker for Cantor Fitzgerald.

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"My office is right next to the World Trade Center," Hobbs said, who is still shaken by glimpses of the area where her father lost his life. "It’s like — oh! I wasn’t expecting that," she said. "I’ve needed to take a step back, take a breath."

Hobbs said on days she's "feeling stressed," she walks along the plaza as it reminds her "that life is precious" and "puts everything into perspective."

Brian Leavey, who was 16-years-old at the time of the attacks, lost his father, Joseph, who worked for the New York Fire Department and perished saving the lives of people at the World Trade Center on 9/11.

"That's how we know the story of his unit. They were at the 78th floor at the time of the collapse of the building," Leavey told BBC News. "They were one of the only units to make it to the fire floor. It was definitely a relief knowing that they did amazing work that day and I'm just so proud of how brave he was."

"He loved being a father and taking care of us," Leavey said of his father, who displayed "big kid" tendencies. "I was very fortunate to have 16 years with him whereas my younger sister only had 10."

According to Leavey, his father's passing made him "grow up a little faster." Now with a kid of his own, Leavey said he wishes his father were around "to fix things round the house" or help with "a renovation."

"It's one of the things I miss every day," Leavey said, according to BBC News. "I'm trying to turn a negative into a positive."

NBC's Today also spoke about the tragedy with two women, Caitlin Leavey and Brittany Oelschlager, who were little girls at the time they lost their fathers, both New York City firefighters, in the attacks.

The women discussed their 20 year journey without their fathers and reflected on how they met. The two girls met one another at America's Camp, a free, non-profit camp in the Berkshire Mountains for children who lost loved ones on 9/11, according to Today.

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"America's Camp was the candle in the darkness for us," Oelschlager told NBC's Today on Thursday.

"It's like friends until the end," Oelschlager said. "From something bad came something great, and this is definitely something great."

Describing the fatal attack, Oelschlager insisted it "was more than just two towers falling," saying that their "entire lives came crashing down with it."

"I just I battled a lot," Leavey recalled, noting how people would ask her how she was doing following the incident. "My first thought was like, 'Well, my dad was a happy person and I want to be happy,' but also knowing that it was OK to have to cry and to have feelings I think was very important for me. I wish I could tell my 10-year-old self now and embrace that 10-year-old self of mine."

"Just to know that there was all these kids there who were from the same experience, and all these people there who just want to make us happy and just let us be kids," Leavey said of America's Place. "It just brought out so much light and sunshine for me, and I just felt like it was also a gift my dad gave to me, because he would always call me his sunshine."

Estimates show that more than 3,000 children lost a parent as a result of the September 11, 2001, terrorist attacks, which killed 2,977 people from 90 different nations in New York City, Arlington, Va., and Shanksville, Pa.