Hey mate. Its always exciting taking the kids fishing.
The boys have provided some really good info. Just to add, sydney harbour night fishing can be very productive. The species i have caught at night include bream, tailor, jewfish, whiting and trevally. I suggest you throw out an assortment of rigs to maximise your chances. Id have a few rods on a running ball sinker and id also have a rod or two out on a float which will be good for tailor and trevally.
Burley in th harbour can make all the difference bringing the fish to your location as well as getting them into the mood to bite. Buy yourself some catfood cans, punch a few holes in them. Put them in an onion bag and throw it out 2 or 3m ahead of where your fishing. When your done pull them in and dispose in the rubbish.