Deliberate mistake: Some of the children that are running in front of the superimposed background were never in the classroom. For example the blonde girl in the blue and white sweater in the middle of the second shot and the girl in the green sweater in the center of the third shot were not there. (01:13:40)????
Continuity mistake: As Melanie and Mitch walk down the hill Annie and Cathy are standing in the middle of the yard with two other children between them and the lounge chair. In the next shot as we see Lydia carrying the cake, the two children disappear and Annie and Cathy have moved to the left closer to the door. (00:51:35)????