This is super common in the US, but I think that's because most expensive colleges are so hard to get into that each kid needs to have an incredible non-academic resume alongside an incredible academic resume. I don't know why Aussies would be so motivated though - my guess is the parents love being a taxi, haha.
That sounds incredibly stressful. To the point where I'm not sure if potential end results are worth it x_x
Some of them just live vicariously through the poor kids, again some time ago I also had one person telling me straight up that they were living through their kid like it was a perfectly normal and good thing (the kid had no say in what interests and activities they wanted to pursue, it was all what the parent wanted).