The Lizard of the Jardin Botanique

Geneva's Jardin Botanique is quite simply amazing and we seem to never go into town without visiting. It has  bespoke wooden climbing frames with rope bridges, an excellent hoist to lift the sand and a lovely lizard and bugs to balance on.

There's a unique carousel, a cafe for a beer by the playground, peacocks roaming and an animal park on the other side of the green. If you have never been here... go!
Beyond the playground there are touch and feel plant areas, a hot house, ...

A childrens' amphitheatre provides story telling opportunities though I don't know if anyone organises them?

Switzerland while famous for being expensive offers a lot of stuff, like this, for free.