When mayor Clark Hill (Tony Hale) is playing his song and supposedly accompanying himself on guitar, his left hand does not move up and down the fret board and finger chords the way it would if he were really playing.
The scenes are supposed to take place about October 31 in New Jersey. However, the trees are all deep green? Fall foliage of golds, reds and yellows of New Jersey starts changing in September with the average autumn foliage peak color in October 19 - 29.
The dialogue includes several modern expressions that wouldn't have been used in 1938, including "time frame" and "inappropriate" to mean an unwanted sexual advance from a man to a woman.
Those big round bales that the kids hide behind were an impossibility in 1938. The machines used to create the bales did not go into production until 1970. The plastic netting wasn't in use until 1998.