PHP properties overloading
You're using private for the variables. That means that child classes cannot inherit them, use them, or redefine them.
Try changing them to protected and I bet it works. You can read more about them in this thread: https://stackoverflow.com/a/4361582/2370483
Make them protected instead of private.
protected $inFile = "Config.ini";
protected $outFile = "Config.web";