But if the person is a stubborn type who feels genuinely innocent he/ she might not open up.

I agree. I want to add:
I would interpret that as a sign or test towards the adult person. Not opening up means, there is not yet enough trust involved. Children test you out very much so. They clearly notice and hear you, when you speak about principles but then don't follow them. So, they give you the great chance to stand to your words; or they reveal your hypocracy just instantly. If you fail, if you get impatient and self-rightious or insecure, they'll find out. If they act innocent and think they can trick you, they'll notice whether you let yourself being tricked. Actually, one knowing smile, without even using words, is enough.

If they are innocent, they cannot be stubborn at the same time, is what I think. LOL

I learned not to speak about principles and try to avoid speaking about them at all, only act situationally in what I think is appropriate for the situation without riding principles. Aren't we all oh so annoyed about others, riding the horse of principles to death? While we have a blind eye when riding them ourselves? ;-)