Revealing mistake: When Anna (little girl who stutters) is crying after being teased, the "tears" on her cheek are obviously fake. They never run or move. I'm guessing rubber cement.
Little House on the Prairie (1974)
1 revealing mistake in The Music Box - chronological order
Welcome To Olesonville - S9-E3
Continuity mistake: Mrs Olsen cleans up the old Hansen house to sell, however it was made the blind school years back and burned down, killing Mary's baby and Alice Garvey.
Laura: I wanted to clean the blackboards extra good today, to make up for being late.
Mary Ingalls Kendall: And talking in class?
Laura: I was not talking.
Mary Ingalls Kendall: You were, too.
Laura: Was not! Nellie was talking and I was answering.
The Voice of Tinker Jones - S1-E11
Trivia: Sean Penn is in this episode, albeit with no lines, always wearing the same blue shirt. His father directed this episode.