My thoughts are that the government probably shouldn't be in the business of telling you what's good or not, even when it comes to the other kids. Mom wouldn't get arrested had instead she rented a rated R movie for the kids to watch. Why arrest her here? Because we've passed some arbitrary morality line where now the government can intervene? Bah.
Or in the words of a law review article: "WHAT IF I WANT MY KIDS TO WATCH PORNOGRAPHY?"
(11 Wm. & Mary Bill of Rts. J. 671)