when I too was 4 or 5, and reading the bible story book, I never could quite grasp the concept of perfection. For me it seemed that if Adam and Eve where CREATED perfect than how would they have had the ability to sin? Also, no one had sinned before them so how would they know what sin was and meant without having had a precidence set? Also I couldnt get past the fact that God would allow Billions of humans to die and suffer to prove a point to the devil.
After that, there were too many things that stumbled me to mention. I just remember that always being in my head from a young age.