Hide the veggies in some kind of carbohydrate and cover it with cheese.
Making mashed potatoes? Mix in some mashed cauliflower, cooked cabbage, cooked kale, or smashed peas. Similarly, you can sneak butternut squash into macaroni and cheese. Quiche is also a dish that hides vegetables well, and most kids seem to like "eggy pie."
Actually, Rachael Ray has some good suggestions on how to get kids to eat their veggies.