Facebook just added an important parental control feature to its controversial kids app (FB)

Messenger Kids, Facebook's messaging app aimed at children between the ages of six-12, is getting a major parental control feature.

The company announced Friday that parents will now be able to activate "sleep mode," which prevents children from using the app at certain times. A parent could, for example, choose put the app in "sleep mode" during bedtime, dinner, or homework time.

When a child opens the Messenger Kids app in sleep mode, they will see this screen. Facebook

Messenger Kids already lets parents see their child's messages and control their contact list, but Tarunya Govindarajan, a Facebook product manager, wrote in a blog post that parents had been asking for more control. The app itself only lets children send messages, photos and videos. It doesn't have many of the features of a regular Facebook account, such as a News Feed, a "like" button, or advertising.

Since Facebook introduced the app in December last year, it has been met with backlash from health experts and child advocates, who have called on the app to be shut down completely. In a letter to Facebook in January, a group of more than 100 organizations and health professionals warned that children under 13 using the app could "undermine children's healthy development."