A 10 minute bus ride from Winterthur Main Station or even better, leave the bus at "Breite" and explore the walking path and "secret trail" - as my daughter calls it - along the walking path through the forest. Beautiful park with lots of animals to see, playgrounds, restaurant, small take away and a large picnic area outdoors. Food and drink is quite expensive so we usually bring our own and have a picnic or light a fire at one of the BBQ spaces around the parc.
Be sure to check the timetable for the bus, there's only one from spring to autumn and not daily - but it's a really nice walk. Depending on the age of children walking takes 30-90 minutes and you can use strollers.