Innocence is a state of grace, a newborn has a clean slate on a foundation based upon two million years of survival instincts. On their own instincts are a means for survival.
Within our DNA is a desire to be the center of all things, and to survive at any cost. This can never be so.

Innocence is the ability to reason about our spiritual nature in a manner where we recognize our own mortality and our imperfections. Children donot have the maturity to understand their own psyche. Innocence as far as it applies to children is a recognition that this ability to discern is not fully developed, hence any self centered behavior is provided a pass.

Innocence as a state of grace is a spiritual virtue. It is acting in a manner that doesnot violate G-d or your fellow creatures.