I took my 12 year old niece down to southern Illinois in the back of my Coupe last year.
Although it was comfortable for her and she thought it was really cool it surely wasn't safe and I had that on my mind most of the way down.
No seatbelt, against the law and heaven forbid if we were involved in an accident and she was harmed in any way.
It was only one time but I will probably not allow it again.