1s Movies (seasonal, monthly, and yearly versions) are only created if at least ten eligible photos/videos have been uploaded to your album for that period. Some photos/videos may not be eligible for use in your 1s Movies, including photos/videos taken in quick succession, other 1s Movies, very short videos, and corrupted files.
Even if you haven't reached ten uploads by the time 1s Movie distribution starts, it's still possible to get your 1s Movie. Once you upload ten eligible videos/photos, the app will automatically create your 1s Movie and deliver it to you within a few days.
1s Movies are initially only visible to the Album Admins (parent members). If you'd like to share your 1s Movie with everyone in your album, first visit the Collections screen by tapping the square icon in the top left of the Album tab. Tap the 1s Movie you'd like to share, then tap “Share in FamilyAlbum”.