When Gavin brings hot chocolate back to his uncle, the cup he holds has whipped cream well above the rim. At 13:52 Gavin's whipped cream is suddenly about an inch below the rim, then at 13:58 it's back up above the rim in time for him to stick his face in it.
When Grandpa Joe is accompanying Kate in a Christmas song near the end, he is shown holding a guitar, but although guitar music is audible, he is not playing.
From Grandpa's POV when he's looking at the photo album, whole pages are decorated including stamped headers, but from the opposite POV the pages appear to be blank as the stamped headers are clearly missing from all the pages.