Summary: a suspension bridge, bouncy castles, and panorama trail in the local mountains.
Sattel-Hochstückli is a mountain resort with lots of attractions for kids, including a huge bouncy castle complex, toboggan run, and a long suspension bridge. Among several hiking options, the panorama trail is particularly nice, with stunning views and a series of interactive educational stations for the kids. Since it's at a lower elevation than most resorts, it's summer season starts very early, in late April and runs through early November. Since it's so close to Zurich, you could even go for a Wednesday afternoon after school. It's a nice resort in winter too, with a long sled run into the valley. See my Sattel in Winter post for details.