Oh my goodness - parents backstage during a show is a nightmare!  I allowed one man to do that and it was a huge mistake.  He would bring soda, coffee, food, etc backstage - even after telling him and the cast repeatedly that was not allowed.  I feel that if parents think their children are old enough to be in a show - they don't need to be backstage.  I always make sure there is an adult backstage with the kids as a monitor - but it isn't a parent of any of the kids.  Most of the parents that raise a stink about it drop their kids off at rehearsals and leave them - why should it be different during a show?  They can sit in the house or lobby and wait if they're concerned!