You can try to spend hours (or even the whole day) together in Technorama.

There, the children can try everything related to science (they have Chemie Lab as well), try to make ice cream, make chocolate, try all the theory of mechanics, physics...

And try to explain all those thing to him.
(Hints : they have the "how things work" brochure nearby the exhibition in English too, just in case you cannot explain it to him )

Or maybe even better, check their website
www.technorama.ch

edit: they are in Winterthur, just about 30 min. by train from Zurich.

Have fun...
Ollie