With the mental health of teens and preteens a prime focus at Tuesday's hearing, Sen. Amy Klobuchar, D-Minn., asked Haugen directly if Facebook hooks users to its platforms at a young age in order to make them more profitable over the long term.

"They know that children bring their parents online -- so they understand the value of younger users for the long-term success of Facebook," said Haugen.

She also said they know children will bring family members to the platform, if not the reverse.

"Facebook understands that if they want to continue to grow they have to find new users. They have to make sure that the next generation is just as engaged with Instagram as the current one, and the way they'll do that, making sure children establish habits before they have good self-regulation," added Hagen.

"By hooking kids?" asked Sen. Brian Schatz, D-Hawaii.

"By hooking kids," Haugen affirmed. "We need to protect the kids."

-ABC News' Zunaira Zaki, Mary Kathryn Burke and Victor Ordonez

Lawmakers on the Senate Commerce subcommittee on Consumer Protection, Product Safety, and Data Security focused on whistleblower Frances Haugen's leaked internal documents showing the media giant found evidence of its harmful effects on young users and its fueling of misinformation but did nothing to address either, putting "profits before people."

For the effect on kids, Haugen said it's a problem previous generations did not have to face.

"Kids who are bullied on Instagram, the bullying follows them home. It follows them into their bedrooms. The last thing they see before they go to bed at night is someone being cruel to them. Or the first thing in the morning, someone being cruel to them," she said.

She added the Facebook "definitely" targets kids as young as eight years old through its Messenger platform, among other tactics.

Haugen said if she had the power, she would establish more transparency with congressional oversight bodies, propose legislation on what an effective oversight agency would look and immediately re-implement the "soft interventions" identified to protect the 2020 election.

"No one censored being forced to click on a link before resharing it," she said.

Sen. Amy Klobuchar, D-Minn., raised the alleged harmful effects of Instagram, which is owned by Facebook, and the data whistleblower Frances Haugen leaked showing Facebook's own research found that more than 13% of teenage girls said that Instagram made their thoughts of suicide worse.

"What did they do? They proposed 'Instagram for Kids,' now been put on pause, because of public pressure," Klobuchar blasted, before asking Haugen if Facebook knows data has shown Instagram also promotes eating orders in young girls.

"Facebook knows that they are leading young users to anorexia content," Haugen said.

An internal Facebook study shown to lawmakers by Haugen that Klobuchar cited said 17% of teen girls said Instagram makes eating disorders worse.

Comparing the social media giant to tobacco companies targeting youth, Haugen said that Facebook is deliberately designing their product to be addictive.

"Facebook has a long history of having a successful and very effective growth division where they take little, tiny tweaks and constantly, constantly, constantly trying to optimize is to grow," she added.

Asked whether CEO Mark Zuckerberg would be the one to dictate the decisions around Facebook's algorithm, whistleblower Frances Haugen said yes, noting his "unique" role in the company, noting he holds over 55% of all voting shares.

"There are no similarly powerful companies that are as unilaterally controlled, and in the end, the buck stops with Mark," Haugen said. "There's no one currently holding Mark accountable but himself."

In her opening statement, Haugen echoed Sen. Richard Blumenthal, D-Conn., in comparing Facebook's reckoning to a "big tobacco moment" and called on the government to take action.

"As long as Facebook is operating in the shadows, hiding its research from public scrutiny, it is unaccountable. Until the incentives change. Facebook will not change," she said.

"When we realized big tobacco is hiding the harms that it caused, the government took action. When we figured out cars were safer than seatbelts, the government took action. And when our government learned that opioids are taking lives, the government took action," she said. "I implore you to do the same here today."

Haugen said that Facebook "wants you to believe that the problems we're talking about are unsolvable. They want you to believe in false choices. They want you to believe that you must choose between a Facebook full of divisive and extreme content or losing one of the most important values."

"I'm here today to tell you that that's not true," she said.

Facebook director of policy communications Lena Pietsch released a statement following whistleblower Frances Haugen's testimony, attempting to discredit her knowledge of the company.

"Today, a Senate Commerce subcommittee held a hearing with a former product manager at Facebook who worked for the company for less than two years, had no direct reports, never attended a decision-point meeting with C-level executives – and testified more than six times to not working on the subject matter in question. We don’t agree with her characterization of the many issues she testified about," Pietsch wrote.

"Despite all this, we agree on one thing; it’s time to begin to create standard rules for the internet. It’s been 25 years since the rules for the internet have been updated, and instead of expecting the industry to make societal decisions that belong to legislators, it is time for Congress to act," the statement finished.

Multiple times during the hearing, lawmakers invited Facebook CEO Mark Zuckerberg and communications spokespersons to appear before Congress and testify themselves.

Zuckerberg has remained silent on Haugen's allegations for days, and multiple senators mocked the billionaire over recent social media posts of him out sailing instead.

-ABC News' Zunaira Zaki