I think it's so easy to encourage children in the arts - just don't squash their interest when they're young. Adore their paintings, their little dances, their little skits. With encouragement - and no criticism, ever, EVER! - they will develop these abilities.
My kids took George Randall's acting class at Celebrity Centre International in Hollywood. This was a wonderful thing for them. You don't have to be a Scientologist to attend the class, and it only costs something like $10 - $15 dollars per class. It was inexpensive enough that all my children could go!
They were not "critiqued" but rather encouraged. They never felt they didn't do well. They simply flourished.
If you're in Southern California, and you have kids who may or may not want to act, I highly recommend this class for all kids - because it increases their ability to communicate.