Responding to Facebook's reply to their earlier letter, Senators Ed Markey (D-MA) and Richard Blumenthal (D-CT) said that Facebook has to do a lot better to protect kids on its Messenger Kids platform, The Verge reported on Wednesday.
"Facebook's response gives little reassurance to parents that Messenger Kids is a safe place for children today," the Senators said.
"We are particularly disappointed that Facebook did not commit to undertaking a comprehensive review of Messenger Kids to identify additional bugs or privacy issues," they added.
Facebook in July admitted a design flaw in its Messenger Kids Service that exposed thousands of children on group chats with unauthorised users.
The concerned Senators shot a letter to Facebook CEO Mark Zuckerberg on August 6, asking him to explain what exactly is happening.
"Children's privacy and safety online should be Messenger Kids' top priority. Your company has a responsibility to meet its promise to parents that children are not exposed to unapproved contacts, a promise that it appears that Facebook has not fulfilled," they wrote.
In a reply on Wednesday, Facebook Public Policy Vice President Kevin Martin said: "We believe... that Messenger Kids complies with COPPA (the Children's Online Privacy Protection Act) and we are committed to continually improving it to ensure that we not only comply with COPPA but also meet and exceed the high standards of parents and families."
However, the Facebook reply failed to satisfy the Senators.
"If Facebook wants children and parents' trust, it has to do a lot better than this. That means dropping Facebook's current whack-a-mole method and taking a proactive approach that makes privacy and security the platform's number one priority particularly for kids," the Senators noted.
The social networking platform introduced Messenger Kids in 2017 and is aimed at kids under 13 years of age.
Messenger Kids is a video chat and messaging app designed for kids to communicate with family and close friends that parents or caregivers approve.
Parents set up and manage their child's Messenger Kids account through their own Facebook account.
Facing the flak from lawmakers and experts, Facebook in February this year decided not to build a new app called "LOL" to let children share and post humorous meme content.
Instead, the social media giant said it would focus more on its Messenger Kids service.
( With inputs from IANS )