I started studying music at the age of five and a half. My older sister was taking piano lessons. When her teacher left our apartment, I would get up on the piano bench and start picking out the notes that were part of my sister's lessons.
I think the first things that are relevant are that things should work well; they should function.
Adults sometimes think children don't think. That's what propels them to order children around. But children do integrate thoughts and make sense of them. When I was a child, I thought about everything in the universe.