Jesus also said that everything He said and did was for our benefit. Why then did He pray to God? To show us how. The problem is two fold: you seem to have no Biblical knowledge, and your son is not really looking for reasons to believe but rather reasons not to, to fend off or reject belief in God. What kind of example have you been to him?
Nobody created God. He is eternally self existent. If you don't believe that you you are forced to accept that either the universe is eternally self existent, or that nothing exploded at some point, out of which everything sprang, and then organic life come from inorganic matter, and order came from chaos, and consciousness, and all of life, is meaningless, a cosmic accident, that has no inherent meaning or purpose. That seems to be what your son wants to believe. Nihilism at its best. But who can blame him? If he has no framework within which to formulate basic beliefs about God, he is without a proper foundation, and ask silly illogical questions like, can God create a rock too heavy for Him to lift? So he can say, then He is not all powerful.