When the daughter looks out of the school building it's raining but when it cuts to Baines there is no rain.
While the Headmaster is talking to Sister of Mine at the gate following the first scarecrow attack, the camera angle switches multiple times. Each time the camera angle changes, her balloon changes positions and string length repeatedly, switching hands, held on a short string in her right hand behind her back, held on a long string in her left hand and blowing out to the side, etc.
During the flash forward at the end, which takes place in 1914, Latimer says to Hutchinson "all those years ago" but is referring to events which took place in 1913, only one year earlier.
One of the boys fighting the scarecrows has a left handed Lee Enfield rifle which didn't exist, revealing it to be a flipped shot.