The parents of two girls who said their children died as a result of a “blackout challenge” on TikTok are suing the company, claiming its algorithm intentionally served the children dangerous content that led to their deaths.

The girls were 8 and 9 when they died last year after viewing the challenge, which encouraged users to choke themselves until they passed out, according to the lawsuit, which was filed on Thursday in Superior Court in Los Angeles County.

The suit claims TikTok knew or should have known that its product was “addictive,” that it was directing children to harmful content and that it failed to take significant action to stop those videos or to warn children and parents about them.

The complaint cites in particular TikTok’s “For You” page, which the complaint says shows a stream of videos selected by an algorithm developed by TikTok that is based on a user’s demographic, “likes” and prior activity on the app. The suit seeks unspecified damages.

“TikTok needs to be held accountable for pushing deadly content to these two young girls,” said Matthew P. Bergman, founding lawyer of the Social Media Victims Law Center, a private law firm created in November to hold social media companies accountable for harming children.

A TikTok spokeswoman said the company would not comment on continuing litigation. But the spokeswoman referred to a statement from December, when People magazine reported that a mother from Pennsylvania said her 10-year-old daughter had died while trying the blackout challenge.

Social media sites like TikTok promote content based on a user’s preferences, said Dr. Lois Lee, a member of the American Academy of Pediatrics’ Council on Injury, Violence and Poison Prevention. Without parental controls, children can be exposed to a range of content, including videos they may not understand, she said.

The academy recommends that parents monitor their children’s social media use and limit screen time as much as possible. When children see many “likes” on a challenge video, Dr. Lee said, they may think it’s safe or fun to try, without understanding the consequences.

“Elementary-school-aged children do not have the knowledge or the insight to realize that these are dangerous things to do,” she said.

One of the girls named in the lawsuit, Lalani Erika Walton, 8, of Temple, Texas, was described in the suit as a sweet and outgoing child who loved dressing up as a princess and playing with makeup. She wanted to be a famous rapper like Cardi B.

She got her first cellphone on her 8th birthday on April 23, 2021, and quickly became “addicted” to TikTok, where she posted videos of herself singing and dancing in hopes of becoming “TikTok famous,” the suit says.

After Lalani was seriously injured in a car accident in which one of her stepbrothers died, she went to live with her stepmother. Without her mother or stepmother knowing, TikTok’s algorithm “directed” Lalani in July 2021 to the blackout challenge, the lawsuit says.

Lalani had bruises on her neck on July 13, 2021, and told her family that she had fallen and bumped herself on her bed frame, the suit says. Soon after, she spent some, if not most, of a 20-hour car trip with her stepmother, sitting in the back seat, watching the blackout challenge, the suit says.

On July 15, 2021, Lalani was found with a rope around her neck, the suit says. 

After her death, the police took Lalani’s phone and tablet, and told her stepmother that “Lalani did not commit suicide,” the lawsuit says. A police officer showed the videos of the blackout challenge to the stepmother and said that Lalani had been watching the video on repeat and had been trying the challenge herself, the suit says.

The second girl named in the suit, Arriani Jaileen Arroyo, 9, of Milwaukee, enjoyed playing basketball and kickball and riding her bicycle.

She received a phone when she was 7 and downloaded TikTok, using it to watch and post videos of dancing and singing. She became “addicted” to the product, the suit says, and started trying “challenges.” Because the “challenges” she discussed involved drinking and eating, her parents believed them to be harmless, the suit says.

In January 2021, Arriani told her mother about a girl in Italy who died while trying the blackout challenge, Mr. Bergman said. Arriani’s mother told her that she should never try such a challenge, and Arriani indicated that she understood, the suit says.

On Feb. 26, 2021, Arriani was found with a leash around her neck, the suit says. Mr. Bergman said that Arriani had been watching a blackout challenge on TikTok. She died that day after she was taken off life support, the suit says.

The complaint cites several other children — including a 12-year-old in Oklahoma and a 14-year-old in Australia — who it says died while trying the blackout challenge.

Dangerous challenges, such as one that involved biting or swallowing Tide pods, have circulated on the internet for years. The suit mentions challenges that involved consuming large amounts of Benadryl or getting out of a moving car to dance on the street.

“I don’t know if they’re any more dangerous than they’ve ever been,” said Zach Sweat, the managing editor of Know Your Meme, an internet database that includes memes and online challenges. “I think the accessibility of these types of things and the way these algorithms work broadcasts it to more people.”