I don't know about where you're living but over here the only time I've heard "kids should be kids" was to a parent who had their kids scheduled to within scant nanometres of their lives.
I had talked to the parent who got told this and they were proudly telling me about how their kids' pretty much every waking moment was at school or an activity or travelling between those and how their day started at 5am or something like that because some of the activities were before school which wouldn't have been a problem if that was what the kid wanted but I couldn't say that confidently
Could just be one of those socioeconomic things though :)
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).
Isn't that why everyone has kids? To live your life again?