Any of the big child actors will probably fit this well, somewhat by default. McCauley Caulkin and Haley Joel Osment both immediately came to my mind. Someone mentioned Natalie Portman in the thread as well.

I'm 100 percent with you on this one. I was a big Sci fi fan going in the first time, and thought I knew what to expect. It ended up being so different than I expected that I didn't really like it at first. Since then, I've come to realize just how great it is. It's a rare occasion where the movie is also significantly superior to the movie for me.