You say that, but literally everyone was a child at some point, so they should know how to portray at least one specific child. For my part, I was a "precocious" child, so I absolutely worried about world peace when I was a kid. And I was not the only one. People really, really underestimate how smart kids are.
At 6 years old, I mapped out my whole town and walked everywhere on foot, back when it was a bit safer. I still remember visiting the cemetery, browsing stores, visiting neighbors, and walking the train tracks, occasionally talking to hobos about life.