Is it OK?
Geez, there was a time my mother was thankful that the bank teller would tell me to stop hanging on the velvet ropes, so SHE wouldn't have to be the onyl one all fo the time!
The reason children don't listen to parents, aside from lack of consequences (oh, my poor baby, he mioght not get an X-Box and go straight to Child Protective Services!),
is that they are the ONLY ones telling them what to do.
The rest of the world has no standards for them!
So I nicely get in the child's face, and screw the parents.
And sometimes, when you say something corrective but kind, you see them listen to strangers.
They hear their parents' voices 24/7, but a stranger is novel, and it embarrasses them.
Mom to a 13 yr old boy, BA Psych, and teacher's asst/Sub teacher. I have no problem being an authority figure to a child I do not know.