Of course, this article reeks of fanboyism (Since it began with a clearly biased comparison between Windows and OS X in OS X's favor.), so you're assuming that everything Apple makes is perfect.

You can harden and harden a PC system all you want, but chances are your kids would know exactly how to break into it or circumvent it completely, or even know how to break it completely.

Does OS X use software like shadow to obfuscate and encrypt passwords? Somehow I doubt it. That's usually the sort of feature Apple loves to leave out of their products. Chances are the kid could EASILY read your password right off the global config, and invoke su -c (Remember, one doesn't have to be a sudoer or have any sort of special permissions to use su, they just need root passwords.) and give themselves just as much permissions as you (Which would be simply something like making themselves a sudoer.) Once he or she is a sudoer or a part of the wheel (Since OS X is a BSD there should be a wheel in place.) and not even have to worry about placing himself in the sudoers file at all, then you can invoke things like PC all you want, he already has the absolute minimum permissions he would need to simply turn it off.

How naive this article is.