Continuity mistake: Near the start, the man's mother puts a yellow dot on his head (just before he gets in the taxi), right in between his eyebrows. After the older woman has kissed him, it suddenly changes to being white and is suddenly a line which goes further up his forehead. And when she kisses him she doesn't touch it so the change can't be put down to her smudging it.
Continuity mistake: In the animated sequence, just before the kids destroy Sister Assumpta's office, Skeleton Boy's cast remnants switches from left arm to right arm and back to left arm. The left arm is the correct side as Tim (who is Skeleton Boy) had his cast on his left arm. (01:20:00)
Suggested correction: Your observation is correct, but this isn't necessarily a "continuity" error. The nature of comics or cartoons lends itself to imagination, creativity, humor, etc. Drawing comics is less tedious these days, thanks to computer programs and "cut and paste" techniques; the chances of a cast accidentally placed on the wrong arm are slim to none. Skeleton Man's "drawing" has many inconsistencies - number of ribs, teeth, finger bones, EYEBALLS or dark holes - with comics, it doesn't really matter.
Character mistake: In the opening scene where Toula describes her house, she says it is complete with "Corinthian columns." The columns on the house are of the "Ionic" style, not Corinthian.