My daughter (7) has always been a good veggie eater so I haven't had to sneak them in, but now that she follows a special diet for autoimmune illnesses, I have had to come up with more interesting ways to prepare the vegetables to give variety since she can't eat pasta, rice, potatoes and a bunch of other foods.
I love the blog Gluten Free SCD & Veggie. Here's one recipe that was really good:
http://glutenfreescdandveggie.blogspot.com/2011/11/butter...
I didn't care for the leeks (too tough the two times I made it) but the cheese sauce came out like a cheesy mashed potato flavor and the butternut squash was delicious. My daughter loved it. Not sure if it would work for all kids but thought I'd mention it.
The only thing with the blog is you have to convert her recipes from the metric system. This site has calculators - http://www.onlineconversion.com/
I have also made a chicken nugget recipe where I've included vegetables. Cook the chicken breast, shred 2 cups and add to a food processor. Add one cup of cooked vegetable (I have used carrots, beans and butternut squash) to the food processor along with a little salt. Process until blended (the recipe said to leave it chunky, but I preferred it blended). Put in a bowl, add three eggs and add some spices (I use cumin and chili powder) and mix together. Spray a frying pan with olive oil and shape the mixture into nugget form. Cook about 6 minutes on each side. I freeze these and pull them out when I don't have time to cook or don't feel like cooking dinner.
Good luck!