I don't have kids, but often babysit my little brothers. They normally eat nothing but cereal, french fries, ramen noodles, and chicken nuggets. When I come over, they want to cook something. I let them pick what they want and take them to the store to get the ingredients. The youngest is 11, his current favorite is pad thai with tofu. They both like tofu scramble, and love to cook anything in the wok. The oldest likes sweets, so we've been experimenting with lower calorie/fat baking.
They do tend to enjoy dinner more if they get to put their hands in it. By far, their favorite thing that we've ever done is make pizza, they really enjoyed making the dough.
Cleaning up, on the other hand, is left to me.