Well, in HTTP pages don't really have parents or children. HTTP is a much less complex protocol than that. The best you can do is $_SERVER['HTTP_REFERER'] (no typo, "referrer" really is spelled wrong in the spec), which usually contains the URL from which the user arrived. This will work 98% of the time, but be warned, browsers are not required to pass along REFERER information, and REFERER information is very easy to "spoof", so don't rely on it for security purposes.
