We went to Sydney for 3 days just because of Vivid and even though weather was bit damp sometimes it was amazing. I loved it all - the big buildings like Opera House and Art Museum, the little displays, the stuff bouncing off CBD buildings, the pop-up restaurants. We walked miles, but it didn't seem like it.
We didn't have our grandchildren with us but they would have loved it. There was lots of interactive displays for children. The was a huge skull and you could stand in front of it and your face became the face on the skull.
The opera house went from being a snake to an ocean scene to thousands of different patterns.