Revealing mistake: You can see the wires on the handgun pointed at the two extraterrestrial children when the bad guys are staring in shock at the "floating gun."
Other mistake: Bobby, Clovis and Celia Bradley find a large gold nugget in a mine. An assayer says gold is worth $15 an ounce and values the nugget at $87,425. That would mean it weighs 364 pounds, more than double the weight of the record-setting 173-pound gold nugget found in 1869 in Moliagul, Australia.
Continuity mistake: As the animated film opens, Charlie Brown's mailbox has a small red flag that is attached to the rear of the mailbox with the flag facing up. At the end of the film, the flag is attached near the front of the box and it is facing down.
Factual error: When the Chinese are loading crates onto the truck with St Paul's in the background, two much more modern buildings are visible either side of the cathedral - out of keeping with the 1910s/20s setting.
Continuity mistake: When Molly dismounts her horse near the end of the movie the blanket slides off. A second later the blanket appears back on the horse.