I agree to an extent, the entire innocence thing isn't about not doing wrong, it's about being so young it's unlikely they've done wrong and changed by doing so. I think the innocence thing stems back to a more primitive time, when men would fight and women would bare their children, through war and sex innocence is lost therefore children are typically innocent until that time.

I personally view innocence as a lack of understanding of the world, because once you finally understand how things actually operate your innocence tends to go. It's an interesting process since your entire belief system can change due to this transition, but this is a very oversimplification of the process, there's various other factors that come into play which could also complicate things further.