What is Worry?

This is question asked by younger daughter asked when my elder one was reading a story to her. The story contained this word which my younger one didn't understand. My elder one tried to explain worry in her own way by showing her hands shivering to indicate that you tend to shake when you are worried. To this explanation my second one said, does it mean you feel cold when you are worried. She interpreted worry to be feeling cold. What a contrasting view?

I wish we (adults) can be in that state of mind and bliss. "No Worries" because we don't know what it means.

As I recollect from Sri Rama Krishna's sayings: "Child like innocence is needed to progress spiritually"