This is why we have the NC17 rating. If it’s a R Rated film parents are allowed to bring their children with them. Take it up with the MPAA review board for their inconsistent and major studio-friendly ratings process. Take it up with theater chains that won’t show NC17 films. Don’t blame a parent for following the rules as written.
So we need more rules instead of a parent with some sense?
No, I will blame the parent. Just because something is legal doesn't mean it's a good idea. That's the difference between being a "parent" and being a "mom" or "dad" - exercising wise discretion for the good of your son or daughter. This woman wanted to see this movie and wasn't going to let the inconvenience of a child stop her.
Maybe the R rating should mean no one under 12 in any circumstances, 12 through 16 only with a parent.
If you want to traumatize and coarsen your small children, do it in your own home.