Continuity mistake: In the scene where Winnie and Jessie are going swimming, when Winnie takes off her dress, you see that her right foot was not completely out of the dress. Then in the next shot, you see Winnie jump in without moving her dress at all, and it is far away from her on the rock.
Continuity mistake: In the scene where the Tucks are having dinner with Winnie, after she was brought to their house, there is a shot of her as she says,"My father has plenty of money." On the far right of the screen you see Angus Tuck lick his fingers and make a downward motion with his hand. Then there is a shot of Angus and he says,"Your father will cut down the entire forest..." and you see him making the same motion of licking his fingers and so on again.