In a stunning moment during a congressional hearing over alleged online harms to children, Meta CEO Mark Zuckerberg turned to parents of victims on the Senate floor and apologized.

“I’m sorry for everything you have all been through,” Zuckerberg said as parents held up photos of their children who have died following sexual exploitation or harassment via social media. “No one should go through the things that your families have suffered and this is why we invest so much and we are going to continue doing industry-wide efforts to make sure no one has to go through the things your families have had to suffer.”

Zuckerberg is one of five executives being grilled in Congress on Wednesday in a hearing titled Big Tech and the Online Child Sexual Exploitation Crisis. The hearing was called to “examine and investigate the plague of online child sexual exploitation”, according to a statement from the US Senate judiciary committee. In attendance are chief executive officers including Mark Zuckerberg of Meta, Linda Yaccarino of X (formerly Twitter), Shou Zi Chew of TikTok, Evan Spiegel of Snap, and Jason Citron of Discord.

The Senate was packed with families of children and advocates, with Lindsey Graham stating “we have a large audience, the largest I’ve seen in this room”. The South Carolina Republican senator accused social media firms of “destroying lives, and threatening democracy itself”.

“I know you don’t mean it to be so, but you have blood on your hands,” he told executives.

Related: ‘They’re addicting kids and they know it’: the attorney challenging social media firms

In opening statements, Dick Durbin said combatting dangers faced by children online had been one of his “top priorities” as chair of the committee and that online child sexual exploitation is “a crisis in America”. The committee chair told executives that their platforms social media and messaging apps have “given predators powerful new tools to sexually exploit children”.

“Their design choices, their failures to adequately invest in trust and safety, their constant pursuit of engagement and profit over basic safety of all put our kids and grandkids at risk,” Durbin said.

Executives appearing in Congress repeatedly highlighted controls and tools they have introduced to manage children’s online experiences and mitigate harm. In prepared remarks, Zuckerberg stated that Meta had introduced more than 30 such tools over the last eight years, including controls that let parents set time limits for app usage and see who their children are following and engaging with online. He added that Meta had spent $20bn on safety and security since 2016 and employed about 40,000 people to address such concerns.

“We’re committed to protecting young people from abuse on our services, but this is an ongoing challenge,” he said. “As we improve defenses in one area, criminals shift their tactics, and we have to come up with new responses.”

A two-year Guardian investigation suggested that Meta has struggled to prevent criminals from using its platforms to buy and sell children for sex. New Mexico’s attorney general sued Meta in early December, alleging the company “enabled adults to find, message and groom minors” for sexual exploitation. Damning internal documents have emerged from the suit. Wednesday’s hearing also comes amid a growing body of reports about negative impacts of social media on the mental health of young people.

Members of Congress highlighted potential legislative solutions to concerns about children online, and repeatedly asked each executive if they supported a handful of bills introduced to address these harms. Central to the hearing is the Kids Online Safety Act – a bill that has been endorsed by a number of advocacy groups but has been criticized by others for serious privacy and censorship concerns.

Snap Inc previously endorsed the bill, and X CEO Yaccarino said for the first time on Wednesday that the company also backs . At the hearing, X also became the first big tech firm to endorse Stop CSAM Act, a bill from Durbin that some groups say also raises civil rights concerns due to its targeting of encryption. Executives from Meta, Discord, and TikTok declined to endorse the bills outright, drawing ire from Graham.

“The bottom line, I’ve come to conclude, is that you aren’t going to support any of this,” he said. “If you’re waiting on these guys to solve the problem, we’re going to die waiting.”