Innocence can have different meanings : religious, legal, moral.
In religion, the innocent is the one who hasn’t been defiled by evil, who is pure (see purity). It’s the state of purity that men had before the original sin.
An innocent person can also be a person who doesn’t know anything about sex, who’s chaste (see chastity).
Innocence is often associated with childhood because when children are born they haven't been confronted with culpability, corruption, or evil. They are considered pure. When they grow up, their innocence can be corrupted.
In a legal way, during a trial everyone is innocent until proven guilty. In this case, innocence can be fake : during a trial the one who’s guilty will do anything to convince the jury that he's innocent, if it works it shows that someone’s innocence can be just an illusion that hides his guilt. Also sometimes innocent people are sentenced for crimes they didn’t commit.
Also, being innocent does not always mean being a good person who never harmed anybody or committed any crime. Innocence can also be a flaw. Indeed, this value can refer to a form of ignorance and naivety. In this way, the innocent is the one who doesn’t realize the flaws of this world, who think that everyone has good intentions which can be dangerous to that person.