Meta CEO Mark Zuckerberg and the chief executives of X, TikTok, Discord and Snap face a grilling by US lawmakers on Wednesday over the dangers that social media platforms bring to children and teens.

The tech chieftains have been convened by the US Senate Judiciary Committee where they will be asked about the effects of social media in a session titled "Big Tech and the Online Child Sexual Exploitation Crisis."

The hearing promises to be grueling for the executives who are facing political anger for not doing enough to thwart online dangers for children, including from sexual predators.

"These CEOs have serious questions to answer about their shameful track records on child safety, and their attempts to keep these failures from public view for so many years," said Imran Ahmed, CEO and founder of the Center for Countering Digital Hate.

Testifying to senators will be Zuckerberg, X's Linda Yaccarino, Shou Zi Chew of TikTok, Evan Spiegel of Snap and Discord's Jason Citron.

"I'm proud of the work our teams have done to improve online child safety, not just on our services but across the entire internet," Meta's Zuckerberg will tell the committee, according to his prepared testimony made available to AFP.

No liability

Under US law, web platforms are largely shielded from any legal liability in relation to content that is shared on their site.

While lawmakers would like to set up more rules to increase online safety, new laws have been stymied by a politically divided Washington and intense lobbying by big tech.

One existing proposal is the Kids Online Safety Act, or KOSA, which aims to protect children from algorithms that might trigger anxiety or depression.

Another idea would require social media platforms to verify the age of account holders and completely bar children under the age of 13 from signing up.

Ahead of their testimony, Meta and X, formerly Twitter, announced new measures to satisfy any political pushback.

Meta, which owns the world's leading platforms Facebook and Instagram, said it would block direct messages sent to young teens by strangers.

By default, teens under age 16 can now only be messaged or added to group chats by people they already follow or are connected to.

Meta also tightened content restrictions for teens on Instagram and Facebook making it harder for them to view posts that discuss suicide, self-harm or eating disorders.

Zuckerberg will tell lawmakers that around 40,000 Meta employees work on online safety and that $20 billion has been invested since 2016 to keep the platform safer.

He will also back legislation that delivers age verification and clear parental control.

'Center of excellence'

X also announced last week, ahead of the hearing, that it was setting up a content moderation team in Austin Texas.

The initial goal of the "Trust and Safety center of excellence" in Austin will be to recruit 100 content moderators, focusing on weeding out child sexual exploitation content and other violations of the platform's rules.

Prior to the tech executives' Capitol Hill appearance, X's Yaccarino was in Washington to meet with lawmakers from both parties on topics including child protection.

X currently has more than 2,000 content moderators, both full-time employees and contractors, the company said.

But when Elon Musk first took over Twitter in late 2022, he imposed huge staff cuts that saw the company's trust and safety teams decimated.

Musk, a self-declared "free speech absolutist," also vowed to remove content restrictions, with numerous banned figures able to return.

For now the only American curbs to the online giants are through lawsuits brought by US states, with about 40 states jointly suing Meta over alleged failures with kids.

Those lawsuits contend Meta knowingly allows users younger than 13 on its Instagram platform, only disabling a fraction of those accounts.

The suits also accuse Meta of concealing internal studies showing user harm on Instagram and Facebook.