If you are looking for a day activity with the kids around Zürich then you might consider Langnau Wildnispark. It's a little bit outside of Zürich but it's completely free.
They have native wild animals there on quite a big area. So you actually are lucky if you see all the animals. I managed to see about the half of the animals they have there - the other half was either sleeping or hiding. Be aware that you have to walk quite a lot there!
Definitely the most popular animals were the bears. They have a whole bear family there with two cubs and they don't mind fooling around in public. Below you can see a photo report of them :)
And just not to keep this post very bear-centered, here are some other animals as well.
Some useful links
- Langnau Wildnispark - https://wildnispark.ch/