I think it takes quite a level of mental sophistication to think about the Earth (as a single entity, as opposed to the bits of it a child encounters). I wonder how many children actually form their own conception of what the Earth is and what shape it is, rather than being taught both the concept and the shape at the same time.

I do remember walking along the pavement at quite an early age and wondering if all the roads in the UK (well, the big island part of it) were linked, or whether there were streets which couldn't be reached eventually by walking along roads from our house. That's another way of looking at the world, and I'm pretty sure I came up with that one myself.