Facebook's new Messenger Kids app is receiving heavy criticism from experts for being potentially harmful to young children.

The messaging platform, aimed at children aged four to 12, launched in December. Facebook and Facebook Messenger require users to be 13 or older to sign up.

Jennifer Shapka, a developmental psychologist at the University of British Columbia, says she is worried about the effect the new app is having on kids' physical and emotional health.

"It's kind of beyond me why we'd endorse yet another way that encourages kids to sit behind a screen," she told Stephen Quinn, host of CBC's The Early Edition.

Canadians spent an average of 24.5 hours online per week, a survey from Media Technology Monitor found last year.

Online safety

But the bigger issue, Shapka believes, is that younger children are not ready to take on the challenges of social media.

Her current research explores the online risks associated with cyberbullying.

"We struggle to help kids and even adults understand how to be socially responsible online," she said. "With younger kids who do not have the cognitive capacity, that's going to be even more difficult."

Safety is always a concern when children go online, Shapka said.

"They are really too young to truly understand what privacy and security means in a virtual, abstract world — they just don't have the cognitive capacity for that," she said.

The new messaging app has several specific safety features. Parents must create the accounts and approve contacts, the child's last name is not required and there are no ads.

"Because it's so safe, in some ways, they might develop bad habits that might transition when they are in the more public spheres," Shapka said. "Cognitively and socially, this just doesn't meet their needs."

Messenger Kids has roughly 45,000 downloads since it launched in December.

Facebook announced this month that its 2.1 billion users are spending about 50 million hours less each day on the platform compared to last year.

Per person, that works out as roughly 48 minutes per day on Facebook compared to last year's 50 minutes.

With files from The Early Edition.