Days after an NBC News investigation revealed how grown men on Pinterest openly create sex-themed image boards filled with pictures of little girls, the company says it has “dramatically” increased its number of human content moderators. It also unveiled two new features enabling users to report content and accounts for a range of violations.

Sens. Marsha Blackburn, R-Tenn., and Richard Blumenthal, D-Conn., sent a letter to the company Tuesday morning demanding to know why the new tools weren’t already available, among other questions.

“It should not have taken national media coverage of such graphic misuse targeting young children to prompt action,” wrote the senators, who are co-sponsors of  the bipartisan Kids Online Safety Act. “This report is particularly disappointing given that Pinterest has branded itself the ‘last positive corner of the internet.’”

Pinterest’s new safety features enable users to report boards and accounts for “Nudity, pornography or sexualized content,” which the site defines as including “intentional misuse involving minors.” Previously, boards could not be flagged at all; individual accounts could be reported only for “Spam” and “Inappropriate cover image.”

As NBC News uncovered, individually innocuous photos and videos of little girls on Pinterest have been compiled by the dozens, hundreds and even thousands into public boards with titles such as “Sexy little girls,” “delicious,” “hot” and “young girls.” These images, which often show the children in bathing suits, leotards and other light attire, are in many cases uploaded to the platform by the kids themselves or their family members, who have no idea how they’re being used.

One woman, whose 9-year-old daughter’s gymnastic videos were saved to more than 50 boards of that nature, told NBC News she was “shocked and disgusted” by the discovery.

“I thought Pinterest was a place to be creative and inspired,” she said.

Her daughter’s profile had been also inundated with direct messages, including “cute ass” and “Mmmm.” The senders appeared to be grown men, based on their usernames and profile photos.

Pinterest spokesperson Crystal Espinosa said the platform has implemented sweeping changes over the past few days, including adding thousands of human reviewers. 

The company has also “taken immediate, broad, and aggressive action to deactivate thousands of bad actors and anyone engaging with content in inappropriate ways,” she said in a statement.

Espinosa declined to give more specifics, saying the company doesn’t disclose details around its Trust & Safety mechanisms to prevent individuals from circumventing those systems. 

Espinosa previously told NBC News that the company would also introduce new age-verification measures at a later date. Pinterest requires users to be at least 13 years old; however, as with other social media sites, many younger children appear to be on the 450-million-user platform. 

NBC News’ investigation additionally found that Pinterest’s recommendation engine was inadvertently curating photos and videos of young girls in light attire for adults seeking out such content. As of Monday, that still appeared to be happening, though some search terms including “young girls” had been newly banned.

The Pinterest account used for NBC News’ initial review — which involved looking at hundreds of accounts belonging to children and the men who follow them over a one-month period — has continued to be served images of little girls in large quantities via algorithmic recommendations in the homepage, its TikTok-style “Watch” tab and through the platform’s suggested-content notifications.

On Monday, within minutes of creating another Pinterest account and interacting with photos and videos of underage girls, the platform curated more of the same in the homepage and “Watch” tab. 

Espinosa said Pinterest has updated its machine learning models “to better understand and distinguish between legitimate uses and inappropriate engagement with content” on the platform. She added that these tools will get stronger over time.

In their letter to Pinterest, the senators were particularly interested in how the company managed the potential for contact between minors and adults, asking to what extent it restricts adults’ ability to message or follow children.

Seara Adair, a mother and influencer who has spent years independently studying Pinterest, believes she intercepted a predator posing as a teen in an effort to groom her 12-year-old daughter on the platform in January.

While Adair wishes the new safety features had been introduced “much sooner,” she called them a big step in the right direction.