I'd like to garner some idea of how many people believe what about the topic of babies being atheist.
The issue is in regard to 'atheism' being a response to 'theism', having some other relationship with 'theism', or having no relationship to 'theism'.
Holding beliefs is very characteristically adult thing to do. As we grow older we get more stubborn, more rooted in what we know and what we think, more closed off to embracing change or new things, making 'beliefs' an ever increasing aspect of who we are and how we identify ourselves. We move from a more explorative stance to a more defensive one.
Young children are the opposite of this, being utterly open to new experiences, ideas and perspectives. They live in questions, and are as free from the burden of beliefs as we get.
So in answer to the OP, its almost the wrong question. Yes i would agree that babies and young (uninfluenced) children lack any theological beliefs, and as such any express a-theological beliefs, because having beliefs like that in the first place is not in their nature. I'd rather label them as pre-(a)theists, in an attempt to convey that they are before such considerations become a major aspect of who they are.