Your belief in what atheism means is irrelevant, what counts is what is understood by atheists who after all is what counts when defining the word atheism, a definition accepted by most dictionaries as opposed to the belief of a pedantic criminal with a home school PhD in I know best cos I said so<quoted text>
"not believing in any gods" is not what atheism means.
It's what atheists WANT it to mean, so that they are relieved any burden of argument.
What it means, and has always meant, is the belief that no god exists.
A newborn is neither an atheist or a theist, as far as we know.
New born babies do not believe in god(s) end of story