Pizza and pizza doughs are definitely good ones for kids.
My son got his start cooking with a package of ramen noodles (that I had bought for when he had surgery, but never used). He didn't like the thought of just noodles, so asked what he could put in it. I let him have at the refrigerator. By the time he was done he had a great soup with hamburger, carrots, broccoli, etc. He took off from there and still likes to experiment in the kitchen. He can follow a recipe, but likes to play with it after the first time.