Like eyrie, I'd let the parent deal with it also, but unlike him I feel as though "my time" starts when class starts not when they walk in the door (some of our students get to class pretty early). I might remind the kids that the eye rolling when their parents tell them to start warming up isn't acceptable, but I'm not going to go any further than that with them before class starts. If the parents ask for suggestions, tips, or help to deal with their kid's behavior before and after class, I'll help them out but not until I'm asked. It's the parent's job to parent, my job to teach during my alloted hour.
"It has been said that politics is the second oldest profession. I have learned that it bears a striking resemblance to the first."- Ronald Reagan