You do not have a frame of reference to evaluate religious / non-religious belief when you are born. And also because you have insufficiient mental capacity to make such a decision anyway. In order for one to be whatever, then it is logical that one is aware. Not being aware that there may or may not be a God is not the same as believing or not believing it when one has given the subject detailed scrutiny. How is it possible to be an atheist / agnostic when one has no understanding of what one is and has yet to develop language, reason, comprehension and memory ? When you are born you only respond to physical stimuli such as hunger and sleep. A baby that has to cry in order to communicate its feelings is not intellectually capable of dealing with anything other than its immediate biological needs. Incidentally Islam teaches that everyone is born a Muslim. That position is equally untenable.
A MIND IS LIKE A PARACHUTE : IT DOES NOT WORK UNLESS IT IS OPEN