The great majority of migrants don't get a job before they leave, unless they're in very senior positions or have a skill that's in desperately short supply, so don't get your hopes up too much about finding a job before you go.
I can understand feeling attracted to Sydney because of better job prospects, but I would be worried if you take that route. We've seen a few PomsinOz migrants heading home because they can't afford a decent quality of life in Sydney. It can be done but at the expense of a long commute, and it's unlikely you'll be anywhere near a beach (did you know that the average Sydney resident lives way out in the west of the city, at least an hour from the nearest beach?).
I just tried applying RRV for my family online. I reached the last page and there is no questions about the children. How does one apply RRV for children? Any help is highly appreciated.