I believe children have mastered the art of play. I find that most adults spend their entire lives trying to re-learn this art. The concept of playing can become so elusive in the humdrum day to day responsibilities of adults. This can sometime make the idea of having fun foreign. I know this because I've had to emerge out of this way of thinking.
You've even seen kids play on a summer afternoon? Their thirst for curiosity and ability to imagine worlds beyond adult reason can extend to sunset. They frolic on their lawn tiring in summer hazes and cooling off with water balloon battles and tons of ice cream.They are free without an limitations to be themselves and they enjoy every minute of it with laughter. It's so hard to be around children who are playing without joining in the fun. Their carefree is too enticing to ignore. What I've come to internalize is this... the over all reaching goal isn't that adults should forget/relinquish about their responsibilities, but find the same freedom and curiosity for life that children have while playing when completing those responsibilities.