I think the store employee could have waited until you were closer so she could speak in sotto voce, but I otherwise don't think the store/employees did anything wrong at all. They're just looking out for their young customers, really.

Besides, if anything does happen to a kid who's allowed to wander the store, the store is looking at gigantic liability and horrible publicity for a while. I'm betting the policy was written by the store's lawyers as a CYA sort of thing.