When in the school yard after Laura falls in the creek, Johnny is sat on the seesaw log with 2 children on the seesaw and a boy behind him rocking it.
When the camera pans the other way, showing Johnny from Mary and Laura's position, the boy rocking the seesaw has disappeared and at least one of the children riding has changed.
The camera immediately pans back again to show Johnny in the front, and the original children and boy are present.
In 'The Love of Johnny Johnson', while Mary and Laura are walking away from the school from 14:30 - 14:38, two boys are visible chasing each other. As the scene continues, the boy that is behind wipes out behind Mary.