TheStatutoryApe said:
They are barring persons from entry based on no other criteria than inclusion in a particular demographic. That's a far cry from giving a discount to persons only of a certain demographic (such as ladies or senior citizens). Do you think they could bar persons from entry because they are black? Female? Muslim? The only reason they may be able to get away with this is because minors are generally considered to not have any but the most basic of rights and it is considered acceptable to generalize teenagers as trouble makers. If they tried to no longer allow a certain racial group in during certain hours because they are supposedly those most commonly caught stealing or causing trouble it would not fly.
Except they're not completely barring them, just requiring they have a parent present. Since minors are, by definition, not considered responsible adults in the eye of the law (i.e., separate juvenile courts), this is consistent with the idea they should have responsible adults present to escort them.
Though, it does raise a question...do they actually need to have a parent present, or any adult? What if someone's grandparents wanted to take them out to the mall? Or aunt or uncle? Could one parent escort their own kids and their kids' friends who are visiting them?
So, I don't think it's illegal, but probably not the best way of going about solving the problem they have...if there's a problem at all. Kids being loud and goofing around in a mall seems pretty normal to me, I'm pretty sure we were loud in the mall when I was a kid too...nobody expects quiet in a mall. If shoplifting is the problem (that was mentioned in the OP), then increase security and crack down on the shoplifters, not all the other kids who are just having a good time and staying out of trouble.
I agree with MIH, by the way, that in a lot of towns, there really isn't much else for teens to do on a Friday night other than hang out at the mall or go to movies. It's lit, indoors, safer than wandering around the streets, has food courts that fit their budget for places to get together for a meal or snack while chatting, and being enclosed, they can be loud without disrupting neighbors in their homes. Where else are they going to go? Nicer, free-standing restaurants are too expensive for kids, parks are closed at sunset (and not really safe at night anyway, owing to the dark places where predators can hide), they can't play ball in the street or a neighbor's yard, because the noise disrupts the other neighbors, they're too young to go to dance clubs and bars. When the last few places they can hang out safely and socialize with friends starts to bar them (malls, arcades), where are they going to go?
I would hope more of those were the 18-25 y.o. crowd (i.e., college kids on summer break) with a few older Batman fans who still stay up that late, and not really teens left on their own that late at night. 
