the reason why Yoojung and Sohyun stand out so much from the rest of the child actresses is because of their height. If you're short, no matter how pretty and good at acting, unless you really have distinctive features that can cover for it, it would be hard to become an "adult" actress when you grow up. Especially if you debut as a child actress. And you need to have an different auras. Yoojung is innocent, cute, elegant, luxurious-looking and sexy. Sohyun too. That's why Yoojung and Sohyun are so different from the other child actresses.