What a wonderful question for a nine year old! I think that perhaps the simplest answer for a nine year old is to say that no one created God. God has always existed and will always exist.
The concept of the eternity of God is the fourth “Principle of Faith” in Maimonides’ formulation of “The Thirteen Principles of Faith”. I will include here an explanation of this principle which I hope will be of help to you (although not necessarily for your son quite yet).
God is eternal and infinite, and everything else is temporary and finite in comparison to Him. A Biblical verse describes Him as, “God, Who preceded all existence…” Another basic concept, which is a consequence of this belief, is that the world was created ex nihilo, from absolute nothingness. This means that space, time and matter did not always exist, but that they had a beginning. The only reality that always existed and will always exist is God Himself.
Aristotle and other Greek philosophers believed that matter was eternal, and that God and matter had co-existed for all eternity. Until the middle of the 20th century, most scientists also believed that the universe was infinitely old and that matter was eternal. In 1925, Edwin Hubble, an American astronomer, demonstrated that every galaxy was receding from the earth. This indicated that the universe was not static, but expanding, suggesting a beginning. In 1965, Arno Penzias and Robert Wilson, discovered background radiation that constituted evidence of the “Big Bang.” As a student of Einstein predicted, if an initial explosion created the universe, remnants of the released energy should still exist in the form of background radiation. They received a Nobel Prize for their discovery, and the paradigm of an infinitely old universe that had dominated the world since the time of Aristotle, was dealt a deathblow. The view that the universe was not “always here,” but rather, had a definite beginning is now accepted by most of the scientific world. When it was first proposed, however, this view generated much opposition and argument, perhaps because, as the famous physicist, Stephen Hawking writes, “Many people do not like the idea that time had a beginning, because it smacks of divine intervention.”