The default starting point is the statement (and the awareness) "I am". That is the beginning of what a child experiences. It is also, curiously enough, the origin of both religion and atheism.

From there one can eventually move toward either religion ("I am not alone.") or atheism ("I am alone.") but it takes awhile before that happens.

Whether it happens one way or the other depends on many, many different factors and experiences.

Many people experience both viewpoints, but at different times in their lives.

Belief in the traditional idea of a "God" is not necessarily required, but may occur in the case of "I am not alone." It may even occur in the case of "I am alone.", but in that case the "God" perceived is seen as a threat, not a comfort. One can base a religion on the statement "I am alone" too...but not a very pleasant one. To be "alone" is strictly a matter of survival. Most religions suggest that there is something more positive and meaningful to aim for in life than just survival. And, to be fair, some of the non-religious people suggest so too...if they are so inclined. ;-) High ideals can be found in either camp.