Boys with guns

Walking past the Port Authority this morning, I saw a child in camouflage holding a rifle. OK, he was probably 20 years old, and a member of the National Guard, but I can't help but think, every time I them, that these young men and women are awfully, well, young for the responsibility they're given. The Guard has been a lot more visible in New York since the London attacks. We are now on "Orange Plus" alert, which sounds more like a calcium-fortified juice drink than something that's going to prevent us from being blown up. What, exactly, are they going to do with those guns? I know they will be the first ones to rush in to help if something does go wrong, but what do they do on a normal day? If they ask, say, my brother, to open his backpack and he refuses, will they shoot him?