Elizabeth Perkins, who portrays Rebecca's mother Janet Malone, starred in the movie Big (1988), the movie poster for which is seen the video store scene.
Kevin's injured knee switches from right to left, then right again. When he shows it to Brian Grazer, it's his right knee. When he's being prepped for arthroscopic surgery, the injured knee is shown as the left one and his right knee appears normal. When he's on crutches, his right knee is bandaged.