I believe what he was saying is that the sophisticated people he knew all had a deep curiosity about life, They were eager to explore new things and ideas and were almost childlike in this pursuit. And many of them truly enjoyed the playfulness that comes from finding something new and speaking of it with others. The mind that does not explore and revel like a child in the new, will wither, grow old and die, even if the body remains. For him, this was taken to an extreme as he explored the world of puppets through his Muppets and how they could continue to change as the world did. They taught children and adults about life. And they still do!

I can't agree any more

I guess it depends on what he meant by "sophisticated". People who are different to put a finger on? People who do unexpected spontaneous things? Which in that case I agree with him; children do spontaneous things as well.

柯云路由本书叫《复归于婴儿》，不错....