I know Sydney much better than Melbourne. The public transport is not fantastic, but it suffices. Make sure that you check the timetable online at
http://www.cityrail.info/ because to some places, trains may only come every 30 to 60 min so don't want to just miss one!
Some places to go around Sydney:
- Taronga Zoo - one of the best in the world, in my opinion. Can't beat the view of the harbour behind the giraffe enclosure!
- Aquarium in Darling Harbour
- Blue Mountains (about 1 or 1.5 hrs away, I think, via train)
If you're doing the Gold Coast, that's where the best theme parks are. For little ones, sea world is fun - similar to Ocean Park but (in my opinion) better, cleaner and more polite

Probably more displays/shows but less rides from memory...
In all three cities, the cities are really nice - I like just hanging out in the city. In Darling Harbour (Sydney), there is a fantastic park with a water play area, last time we were in the city, we spent about 1-2 hrs with my daughter just running around in the water in her undies - reminds me of my own childhood!! Brisbane has a gorgeous area like that too, with artificial beaches etc. I forget what it's called but I love it!
Circular Quay (Sydney) is beautiful too, leave a bit of time and watch the street performers. I love them as well. Make sure you catch a ferry or two, can't beat Sydney Harbour!
End of Sept is just starting to warm up but not really THAT warm yet. Personally I like warm better than cold so I'd prefer Sydney/Gold Coast to Syd/Melbourne. The weather should be great, it's a nice time of year.
There's some of my ideas - hope that helps
