"Even a newly self-aware kid will deduct that the Earth is round if they recognise the shape of the moon & the sun."
Highly arguable. First off, what kind of kid? How old and mature? Is he ignorant or is actually interested in truth? Most kids, you see, tend to argue down to the very bone on what they choose to believe. Exaggerating things to support their argument is nothing new to them. That, and also the fact that most kids won't even think about whether the earth is round or flat since all they see is flat surface and sea and everything is pulled down by something so-called gravity. Kids believe the earth is round because they're forced to believe so until the moment they come to accept that as a fact when they grow up.