Facebook may be feeling the pinch from teen-focused, mobile-first social networks like Snapchat, as CFO David Ebersman said on Wednesday’s earnings call that Facebook “did see a decrease in daily users specifically among younger teens,” though he prefaced that saying “usage of Facebook among US teens overall was stable from Q2 to Q3.” This is the first time Facebook has reported real trouble with teens. Facebook did say that “We remain close to fully penetrated among teens in the US,” (eww, terrible phrasing) and noted there wasn’t a ton of data supporting the drop with young teens. On the data, Ebersman said “This is of questionable significance … but we wanted to share this with you now because we get a lot of questions about teens.” The grim notes on young teens come after Facebook had denied losing luster with teens last quarter.