Jeff, it is not shoplifting or keeping an eye on them.
Teenagers as a group tend to be a pain in the ass. They all want to show off how cool they are. So they bother other customers or mess up your store. It doesn’t mean they’re going to steal from you.
Not letting a dog in a restaurant is simply because dogs CAN be annoying if they don’t behave. The only solution is to ban all dogs, because it’s hard to decide which dog will behave. It’s not because they dislike dogs, they want their customers to be satisfied and a constantly barking dog won’t do that.