There's a passage in the Bible from Corinthians that people quote now and again that goes:
"When I was a child, I spake as a child, I understood as a child, I thought as a child: but when I became a man, I put away childish things."
Well, it's exactly that attitude which is why so many adults find it difficult just to let go and have simple fun. Here's a quote I enjoy much more; it's from Keith Johnstone, one of the trailblazers of modern improvised theater:
"I began to think of children not as immature adults, but of adults as atrophied children."