Islam is instinctual, there is a hadith that says a newborn is born instinctually, unless his parents raise him as a jew, christian or a majoosi(it's an arabic word for people who worship fire).
So if you let a baby grow up with no teaching of any religion, he/she will become a muslim eventually.
But then when I was just 5-7 years old & I was told that god(allah) created everything, why did the first thing that came to my mind was "who created god?" ? Wasn't I supposed to instinctively accept the main idea of Islam without questioning?
And when I asked them that same question, they asked me to ask god for forgiveness, and this question comes from satan who manipulated my mind and let me have these thoughts. And that I have to promise god not to have that sort of thoughts so he would forgive me!