Given the definition that self-confessed atheists prefere for the meaning of privative a (
http://en.wikipedia.org/wiki/Privative_a), the view that we are born atheists is indeed the logical consequense, given the theoretical presupposition of 'tabula rasa'. Equally we could say that we are all born asubjects, aobjects, apersons, a-americans (or what ever anationals), a-atheists, -a-atheists, ...a-a-atheists and what ever adefinitions and adefinables, and it is not until we are tought to do so that we start to believe in definitionism.
Of course, the presupposition of 'tabula rasa' should be open to sceptical scrutiny and not accepted without philosophical and empirical questioning. There is also another obvious case for atheistic infants besides the tabula rasa -hypothesis. E.g. supposing that memory of past lives does indeed happen, and supposing that Buddhism is atheistic philosophy(/-religion), in that case Tibetan buddhist tulkus like Dalai Lama are (re)born atheists.
QED