Seems worth a try. I'd try GRMS instead (it's just $80 for the family license for 5 yrs I think). Keep in mind many FRS/GRMS radios tend to use rechargeable batteries which self-discharge pretty quickly.
Yes , at least GMRS, FRS is a joke, we tried them before and couldn't hear each other on the radios even though we could see each other through the woods. You can find them AA powered, though a little larger, so you can drop in some low self discharge batteries.
The big thing I'd want improved is the PA announcement to evacuate. I would really try to get them to give a better description of their understanding of their threat. Something like "there is a report of an explosion up the street, we have no more details" is infinitely better than "evacuate the building now".
-john
The PA announcement having more detail may not be doable. In my building its a simple recording that kicks off from any number of inputs like the manuall pull fire alarm. Could be the same there, someone could pull the handle and the alarm and evacuate recording would go off with no way for anyone to give more details. Also giving more detail could induce panic, if the message is the same every time then no one knows if its something real or a drill. We get e-mail reminders that our company does require drills and then we usually will have one soon after, so they are not scheduled at a certain time.
Does your son have friends in the day care (I forgot what his age is now)? Many day care places like to have volunteers, since your close by can you volunteer as an emergancy planner for the day care and talk to them about go kits and have a bag stocked in the day care that you can grab and take your son and others to safety?