Although story is supposed to be set during summer vacation, the film was clearly shot in winter as actors' breath frequently condenses in outdoor sequences and there are no throngs of tourists as you'd expect to see during high-season.
During Aunt Albertina's entrance into hotel lobby, color of blue and pink hair ribbons on her two dogs shifts from dog to dog long shots to closeups.
When Gidget and Moondoggie are by the river on their first day in Rome, he calls her "Midget" instead of "Gidget"