Temporary Suspension of Disbelief

The original "The Parent Trap" is on television right now. I love this movie, cheesy and cliched as it is. The split screen is very well done, especially considering the era in which the movie was made. However, I always get stuck on this point: Why didn't Susan and Sharon notice that they look incredibly similar? I mean, if I were sent to summer camp and met a girl who looked exactly like me, only with a different hair cut, I think I'd notice the strange coincidence right away. It's kind of like how no one ever notices that Clark Kent and Superman look really, really similar, except for the glasses.