Telephone
The kids graduated from high school in 1937 and the film ends before the end of World War II. Other than that we are not given specific dates for many of the different scenes.
Regardless, the scene in the hotel room in Florida, Tim is speaking with Vicky on the telephone. I am not an expert but it seems to me that the telephone that he is speaking on is a style that did not exist at that time. (An anachronism)
Can anyone else give me back me up on that?