Do you also think that dogs are atheists, fetuses and corpses? What about plants?
If they lack a belief in god, then yes.
I am not sure if babies can "know", if they can't. they would not be considered Agnostics either.
I think they might but I am not sure.
They are atheists. Atheism deals with what you believe. (a)Gnosticism deals with what you can know.
IMO you need to be able to know, to not know. So no.
Your opinion is wrong. Atheism deals with belief.