Snapchat may stand to gain the most from young users on social media in 2018.

Facebook has gained a reputation for being the network of choice for moms, dads and even grandmas — which can be a turnoff for the younger set.

According to eMarketer’s latest forecast, that turnoff could grow even stronger: The network will shed 2 million users under 25 this year, the firm said, and the company’s Instagram platform might not catch them all.

EMarketer said Facebook’s tally of overall monthly average users is expanding. But the research firm chalks up that growth to older users. Its latest social media forecast predicts that, for the first time, less than half of U.S. Internet users ages 12 to 17 will use Facebook this year.

“In 2018, the number of U.S. Facebook users ages 11 and younger will decline by 9.3 percent,” eMarketer wrote in an report covering the results. “Additionally, the number of users ages 12 to 17 and 18 to 24 will decrease by 5.6 percent and 5.8 percent, respectively. This is the first time eMarketer has predicted a decline in the number of U.S. Facebook users in those age groups.”

While Instagram can catch some of the runoff, the firm pointed out that it won’t capture everyone.

Cue Snap Inc., which has been experiencing something of a comeback. The report predicts Snapchat’s growth in users under 25 will outperform Instagram this year, at 1.9 million users versus 1.6 million, and that it will continue to boast more users ages 12 to 24.

Granted, that won’t knock the giants off their perches. EMarketer estimates that Facebook will clock in with 169.5 million total U.S. users and Instagram will hit 104.7 million users, which easily top Snapchat’s projected 86.5 million users. But the overall numbers overlook the nuances in youth trends — and the new challenges that lie just beyond that horizon.

“Snapchat could eventually experience more growth in older age groups, since it’s redesigning its platform to be easier to use,” said eMarketer principal analyst Debra Aho Williamson. “The question will be whether younger users will still find Snapchat cool if more of their parents and grandparents are on it. That’s the predicament Facebook is in.”

Of course, Facebook might not see things this way. The company declined to comment on the record for this story, but it seems to write off juxtapositions with Snapchat growth as apples-to-oranges comparisons. And regardless of internal metrics, it doesn’t break out user data by age, at least publicly — which, in itself, may speak volumes.