This is a recurring discussion that atheists have been debating for, at least, the fifteen years that I have been monitoring and participating in atheist forums - I have been dedicated to search for the resolve of these issues, because the unresolved issues form the dogma that maintains the stall that atheists perceive of society.
I am of the opinion that we are born as a 'clean sheet' neither theist or atheist. To be an atheist one has to be aware of the concept of theism and then to reject it.
Does one need to have knowledge of something and then conciously reject it to be "without" it? Is not the person that has no knowledge of even the concept of god not also "without god"? Does the newborn baby have any such concept?
This is the old trouble with the label, it inherently assumes the possible existence of a god to be able to reject it. "Realist" might be better label, a newborn is hardly that!
Tabula Rasa - blank slate was described centuries ago
https://en.wikipedia.org/wiki/Tabula_rasa. I am very confident that, "secular," is the correct word for classifying persons without any indoctrination, or bias - and I will argue that it is impossible to be without indoctrination or bias upon reaching consciousness (of competing doctrines).
The child is born secular until indoctrinated by the teachings of the guardian community - culture.