How Can I Tell a Male Who Has Never Been a Father That I Know What I Am Doing?

i do agree it sounds like he does love this child ,she is 6yrs
she can talk so just try and explain to him if he is wondering what her day was like ,just ask her at this age kid are most likely to give lots of detail of there day,two things with doing this 1,he will no how her day was and 2, he will have great communication with her.and when you do watch her let him know that you are happy that he cares so much for this child
and there are not many boyfriends that care so much for someone else's child,it will give him confidence and reassure him that his positive for this child is great for her and him

He may have been stressing it so the *child* can hear it, and know what's expected. I'd say, unless he starts accusing you of actually doing something wrong, or contradicting what the child's mother has told you, just let it go.

It is apparent that this man cares very much for the child. I would try not to take it personally. If he didn't trust your judgement, I doubt he would leave her with you.

It sounds like this boyfriend really cares about this child and yes, being a father figure sounds new to this man.
Just let him know the next time you see him that you have children of your own and that you understand that he cares for this child and worries while he is gone from her. but that she is in good hands.
tell him if he has any questions or concerns about the child or the care that she is getting with you to let you know.
this should make him feel better.
it sounds like that there might be other people in the man's life that dont know how to care for children.
Take care!