Continuity mistake: After the Ballet, Alfalfa is being chased by the two bullies and Alfalfa is carrying a handkerchief that Darla gave him. He dives into someone's pool and swims across. When he gets out, he picked up his underwear but the handkerchief is gone. In the race, he has the handkerchief back.
Continuity mistake: When the kids run into the shed to change to their firefighter outfits to fight the clubhouse fire, it is glaringly obvious where they stopped the film and started it again: the sky has changed and is much more dim than when they entered.