Have you ever (been) asked this question?
The first Hakdamah (introduction) is God cannot be proved.
… The metaphysical naturalist cannot defeat hard solipsism, and cannot induct logical induction itself… Ergo, anything he says and/or thinks (including “Good morning”) is either viciously circular or violates the law of non-contradiction.
Finally, I would say this:
‘If God created the world, who created God?’ is an expression of reverent amazement masquerading as a logical paradox. Since the simple meaning of the word “God” indicates “uncreated”, it is as though one said “But love is too wonderful to be real!”, or “How could anything be so beautiful!”
God with a beginning is an oxymoron and violates the law of non-contradiction. So the supposed “question” is but a special case of the infinite regress, which rejects all claims to human knowledge (again, by the way, bumping against the law of non-contradiction). With nothing to stand on, one can always ask “why” and “wherefore?”
Good luck with that…
[This refers to the standalone question “But who created God?” If you heard the question in the course of playing with “Everything that has a beginning has a sufficient cause”, etc. etc., it’s your own mess; don’t ask me to clean it up.]