Hello ,

I also agree with the others that Swiss in term of safety is the paradies compare to other countries. Kids can walk alone from school or you can walk alone late evening and nobody will stop you. But I think the area you should avoid like in any other country, is the area around main railway station(Hauptbahnof here). I would say like Langstrasse. It is hard to live there with kids, cause you see drug dealers, hookers and any other kind of "dirty" people. and the view is not so attractive there, dull and dirty.
Actually Zürich is full with nice areas, where you can find all activities you need. I wish you good luck in your search and enjoy your stay in Switzerland!