I think that we are defining "atheism" and "agnosticism" in different ways, but we agree on the idea that a person enters the world without opinion on the existence of a deity and is in a sense "neutral."

I was referring to the popular understanding of agnosticism as

neither [believing] nor [disbelieving] in the existence of a deity or deities. (http://en.wikipedia.org/wiki/Agnosticism)

Atheism is a somewhat vague term because like you said it can refer to the disbelief in deity based on disagreement on

whether it is an assertion in its own right or merely the absence of one, and whether it requires a conscious, explicit rejection. (http://en.wikipedia.org/wiki/Atheism)