The reason they are inside is because their parents have put the fear of the outside world into because it is "such a bad place". Don't talk to strangers or you will be kidnapped( BTW less then 1% of kidnappings are people the kid didn't know) don't be out after dark or you will be mugged or murdered, zombie apocalypse, don't fall you might break a bone or crack your head on the concrete, ect.
Truth. I may be in the minority on this one but I am excited for a zombie apocalypse...I think if mankind's extinction is inevitable then that's the way it should go down...and there is no sense in wasting my stockpiles of ammo!