When Jack is shaving in "Chess Lessons", at one point a bit of shaving cream is still visible on the side of his face, and though he does not wipe it off, it's gone in the next shot.
During the first half of the season, Bobby is referred to as being 13 years old, but beginning in episode 1x11 they began referring to him as being 12 years old, which he remains for the rest of the season.