Deliberate mistake: The little red-haired girl boards a bus with other children who are headed to summer camp. As the bus drives away, there is nobody in the driver's seat. This movie maintains Charles Schulz's policy of never showing adults in his comic strips or animated television specials, but a bus driver could at least have been depicted in silhouette.
Continuity mistake: This is near the end of the movie when Charlie Brown is running to catch the Little Red Haired Girl before she boards the summer camp bus. As Charlie encounters obstacle after obstacle he runs into the "Kite Eating Tree" and asks for help. A kite falls down and he gets tangled up in the string and he is pulled away. There is no ball of string at the end. Several cuts later when everyone is amazed that Charlie Brown is actually flying a kite and following him, a ball of string magically appears and Charlie Brown is holding it while running and flying the kite.