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It's a grown-up problem for Facebook which needs young users to develop the habit of checking Facebook so it can show them ads well into adulthood.
EMarketer forecasting analyst Oscar Orozco says teens and tweens, seem less engaged on Facebook, logging in less frequently and spending less time there. Instead, he says, they are migrating to Snapchat and Instagram.
What's more: There are now "Facebook nevers," children becoming tweens who are skipping Facebook altogether.
Snapchat usage is expected to increase this year, with the U.S. user base to grow 5.8% to 79.2 million monthly. EMarketer increased growth projections for all age groups except the oldest, with the biggest jump in young adults, ages 18 to 24 increasing nearly 20%.
Similarly, monthly Instagram usage in the U.S. will grow 23.8% in 2017 to 85.5 million. Within that figure, Instagram will expand its user base among those under 12 years old by 19% and those ages 12 to 17 by 8.8%.
Facebook declined to comment.
"Both platforms have found success with this demographic since they are more aligned with how they communicate – using visual content," Orozco said in an eMarketer blog post.
According to eMarketer, this marks the first time eMarketer has ever predicted a decline in Facebook usage for any age group.
For years there have been warnings that Facebook was losing its cool with young people.
Facebook bought Instagram in 2012 for $1 billion in search of the fountain of youth.
In 2013, Facebook's former chief financial officer David Ebersman admitted that young teens were hanging out on Facebook less frequently.
Subsequent surveys found that Facebook was still alright with kids.
When Facebook's $3 billion-plus takeover offer was rebuffed by Snap, the parent company of Snapchat that is popular with teens, it opted for the next best thing: cloning the buzzy chat app's features on Facebook and Instagram.