Well said, children are naturally so creative and insightful in my experience. 'Grown up thinking' from my observation is systematization, often involving putting ideas into a grid of sorts. Stay in grid thinking for too long and you start to believe that the model is more important than reality.

Terence Tao has a great example of kids natural intelligence and creativity: observe small children playing in a schoolyard, they'll often play a game of "who can say the largest number" -- kids will throw out all the numbers they know until one of them has the insight that no matter what number the other kids say, they can always win by going "plus one" to the last number said. That is natural insight about the nature of unbounded sets.