What prevents a child revealing the truth?
I was thinking about this one and it occurs to me that it depends on the context.
What truth is the child not revealing? The truth of something he did, or the truth about what someone else did?
Think back to when you were a kid, if I did something wrong, I might not tell the truth to try and avoid the punishment I knew I deserved.
In the other case, you don't want to reveal the truth about what someone else did, because they threatened you with bodily harm if you did.