Most people would agree that children are generally more creative than adults. Children draw more, ask more questions and come up with interesting ideas. There are two commonly held theories about why we lose our creativity as we age.
The first theory is that as we age, we become more and more aware of practical constraints such as gravity or economics. Working within these constraints prevents us from fully utilizing our imaginations. We must suspend our disbelief in order to be mentally playful.
The second theory is that our culture socializes creative properties out of people. When we are young we are encouraged to draw and play, but as we get older more emphasis is placed on more cerebral activities such as math and reading. Children are slowly trained that being able to do arithmetic is more important than being creative.