Children love to be creative, it is in them from birth! At young ages they want to "make things", but its not the "things" they are loving, but the process of making them.
For instance, 3 year-olds usually stir all their paint together on the canvas until it looks like a chocolate shake, and then want another canvas, and another...For this reason, we recommend that children be 5 or older to take a children's painting class.
For my own children I'd put 7-8 sheets of paper on the bench, give them an ice cream pail lid with tempera paint (washable!) and a brush, and they'd happily fill the pages and want more paper. My beautiful grandchildren (above photo) can come to a real painting studio to do their creating:)
Letting children tell you about their creations is also important, as its not always recognizable, and they may be disappointed if you don't see what they see.
Giving your children creative opportunities without judging their results (or minding a little mess!) is perhaps the best way to nurture their creativity.