Hiding veggies is a very easy thing to do. I know some experts don't recommend you hide vegetables, but at the end of the day, especially with kids, you're responsible for their nutrition, so I always hide veggies in a sauce.
What is particularly useful is tomato based sauces. You can easily hide the sweeter vegetables in tomato based sauces, whether you're using it for pizza or pasta. I usually always blend cooked carrots, onions, sweet chilis, peas or spinach in the sauce. Beware that if you use too many green coloured vegetables it can dirty the red color of the tomato based sauce.
I have found it a great way to get vegetables in to my fussy children. They think they aren't eating their veggies, I have the peace of mind knowing that they do, and there's no arguments. It's a win-win!