If I start a campaign, billboards and all, saying that my doctor is a pedophile once convicted of rape in Australia who has been also implicated in organ trafficking (when she's actually very wonderful) then I should be held liable for the damage to her career and reputation, at a minimum.
Slander and libel are illegal, but the threshold at which the law takes effect depends on how public the target is.
As such care has to be taken when making statements about a private citizen, e.g. "Mr. X is [something horrible]", but one can say almost anything about a public figure like the president, or senators, without fear of legal trouble.
And that's just how minors are treated.
Based on your example, I guess that's not how it always works, but there's no reason in principle why the laws and legal standard around it could not be fixed to be more fair.
There's also the concept of a "limited-purpose public figure", which means that just commenting on something can make you a public figure in certain contexts. For example, if you were to merely say that I was a pedophile, you probably have defamed a private individual. However, if you replied to this post with something like, "You probably just think defamation law is good because you're a pedophile that doesn't want to get caught"; defamation law could take your side. After all, I joined this particular controversy by commenting on it, that makes me a limited-purpose public figure. So even if you're not a public figure, it's very easy to accidentally become one.
Australian views on this should therefore NOT be taken as a norm.