They can be great teachers to adults who have lost their sense of play. A child can sit alone in a room and completely abandon themselves to the moment. They make weird sounds, imagine worlds, pretend to be someone else, run, jump, and move their bodies. They naturally follow their interests, and love new experiences. The spirit of play is alive in them.
Adults can rediscover their sense of play.
It's that simple. If you're all uptight, and feel like your life is dull, just play. Make weird sounds in front of the mirror, make funny faces, chase your kids around the house, sing and dance, make up a story then try to make others believe it's real, make up a joke, etc. The first step may be an enlightening one. Play hide and seek.