Zürich: The churches come to my mind first - Fraumünster, Grossmünster, Peterskirche.
The old town is actually very beautiful, your kids will most likely enjoy a stroll (window shopping).
The funiculars / mountain railways like Polybahn, Dolderbahn, Uetliberg train take you to nice viewpoints (lake, city, mountains in the distance.)
Archeological sites (mostly underground) from stone age over Roman times to Medieval times can be visited if you get a key to those sites from the city authorities. Link here, I only found it in German but you can try Google translate:
https://www.stadt-zuerich.ch/hbd/de/...a_fenster.html