Other mistake: After Marie and Fritz take off to the Christmas tree in the first scene where they talk to their parents, Fritz is shown pulling toy soldiers off the tree to play with. In the first shot of the tree, Fritz stands back up from the toys he has already taken down and reaches for another one. There is nothing in his hands. The spot he reaches for has nothing in it, but as soon as his hands reach that part, a toy soldier suddenly appears in the spot he touches, without the camera cutting. And then in the next shot he bends down and puts his hands on his toys as if he is placing the toy soldier with the rest, but there is again nothing in his hands.
Other mistake: At the beginning of one of the school years, there is a sign on the front of the school that says, "Welcome back Class of 1980". A few months later, in December of that same school year, John Lennon is murdered. Since that class is graduating the following spring, the sign should have read "Welcome back Class of 1981", not 1980.