Maybe I'm missing something but here is how I see it.
Babies cannot process logic on the level of adults and not only don't have a belief about there being or not being a god, they can't even comprehend the idea of a god.
At some point, most humans gain that ability and subsequently are presented with conflicting claims or arguments for theism. If the two sides of the argument are presented before the ability to process it, then I suppose one would have room to argue what the default position would be.
On the other hand, if prior to gaining the ability to process the logic, one were never presented with one or the other, that person would be in fact an atheist. They would have to ponder SOME logical question to decide, 'Oh, there must be a god.' I'm pretty sure one doesn't gain a belief in a theistic entity by default without either being presented with that belief by others, or (in what I would think would be VERY rare circumstances) by having never been presented with the concept, then gaining the ability to reason, and upon pondering a question like, 'Why am I so perfect?' or 'How did complex ecosystems come to be?' coming to an independent conclusion that some entity was responsible that has 'godlike' properties. Under those circumstances, one wouldn't know the term, 'godlike' but the properties attributed to 'godlike' would be understood.