The question of whether everyone is born an atheist depends on how one defines atheism and the concept of belief.
Atheism is generally understood as the absence of belief in gods or deities. By default, infants and very young children lack knowledge about the concept of gods and religions. They have not been exposed to religious ideas, rituals, or doctrines, and therefore, they do not have a belief in any specific deity or religion.
In this sense, you could argue that infants are born without any religious beliefs, making them functionally "atheist" in the absence of a belief in gods. However, it's crucial to note that atheism is typically considered a position adopted consciously by individuals who have considered the concept of gods and chosen not to believe in them. Infants and young children cannot actively identify as atheists as they lack the cognitive capacity to understand and make such decisions.
It's essential to differentiate between a lack of belief due to ignorance (in the case of infants) and an informed position of non-belief (in the case of individuals who have examined religious claims and chosen atheism). People's beliefs are shaped by cultural, social, and personal factors over time, which can lead to a wide range of beliefs or non-beliefs in gods and religions.