First, and most importantly, is chaining them up in a wet, damp basement. You should do this a few hours every week. Personally, I have found that Friday and Saturday nights work best. Not only do I get to go out and have fun, but I am giving my future artist an experience that they can draw from to create great art. And that's the key, trauma.
The next step helps if you are friends with a funeral director, but there are ways that you can do this even if you are not. You need to lock your child in a room with a dead body. If it is a special day at the undertakers, you can even do it with two dead bodies in the room. You can pretend like it was an accident and your aspiring artist was playing and got lost, but you know that you are doing what it takes to make society better.
One thing that usually prevents an artist from developing into who they are designed to be is their parents. They give in too easily to the screams and cries they hear from the basement, the locked room, or feel guilty about terrifying them. Don't fall prey to this. What you are doing is important for the sake of culture. Don't give up.
And I'm open to suggestions. Maybe you have figured out better ways to nurture a young child's artistic spirit. If so, please share.