ABC News' Suzan Clarke and Kelly Hagan report:

Nelba Marquez-Greene will never forget the day that her 6-year-old daughter, Ana, was killed in a horrific attack at Sandy Hook Elementary school in Connecticut.

"In my heart as a mother, it will always be Dec. 14, except it's 7:30," she said in an interview with "Good Morning America's" Lara Spencer.

At about 9:30 a.m. on Dec. 14, 2012, Adam Lanza entered the Newtown, Conn., school. He opened fire, killing 20 first-graders and six staffers before fatally shooting himself in the head as first responders were arriving.

FULL COVERAGE: Newtown, Conn., Elementary School Shooting

Marquez-Greene and other victims' family members were in Washington, D.C., this week to mark the six-month anniversary of the shootings and continue their push for stricter gun laws. Some family members met with President Obama Thursday, while others, including Marquez-Greene, met with U.S. Senators Wednesday urging them to continue the fight for gun law reform.

Afterwards, three of the families talked to "GMA" about life after the tragedy and their ongoing commitment to mental health and gun law reform.

"I feel like it's my responsibility as Ana's dad to do something that honors her life and, in some small way, maybe prevents some other family from having to go through what we've had to go through," Jimmy Greene said.

Even after the Senate voted down a background check provision in April, the families said they would not give up their fight to keep guns out of the wrong people's hands.

"We're in mile one of a marathon, so we're going to continue to work for this," Mark Barden, whose 7-year-old son, Daniel, was killed, told Spencer. "And we're going continue to try to convince people and influence people that this really is the right thing to do."

Many of the families met for the first time as they were waiting at the school for word of their children's fates, but they've since become united in their heartbreak and their determination.

Jackie Barden said they weren't "strangers anymore. Now, it's like family."

The Bardens and Greenes have become involved with the Sandy Hook Promise Organization, a non-profit group that is working to prevent similar acts of violence - and they continue to live in a community marked by memories.

Spencer asked if they had ever considered moving away.

They all shook their heads and said they would not leave.

"We loved it here from day one. And we love it all the more, now," Mark Barden said.

Added Marquez-Greene: "That young man made a very bad choice and took my daughter's life, he's not taking anything else, not taking my house, not taking my community."