Re: i need urgent help : i'm demonically possessed

Why would GOD permit a demon or Satan to control his "children"?

Problem of Evil.
If God does not allow evil to happen, then free will is no more, and the merit of living a virtuous life disappears.
(The point has been explored in a more modernly accessible context by robot theorists too)

Now, notice that I am granting you to frame this under the prevalent theology within Christian churches.
a) Some religions, including some Christian churches, do not believe Satan (or forces of evil as applicable) has the power of possession.
b) Some other non-materialist traditions without a monotheistic God in the sense of Middle Eastern monotheism, allow possession to happen without conflict because they do not assume omnipotence of good, or even prevalence of good, against evil. (This is of course another solution to the Problem of Evil. It is just not acceptable to Middle Eastern monotheists)

But all this talk about Exorcisms just made me want to read a grimoire or two.