Depends on the age of the child.
Put them on your plate and say how delicious they are, then say, "Oh look, you don't have any on your plate." Don't focus on how they HAVE to eat them but make it more about wanting to eat them.
Hide them - see "Deceptively Delicious" and other similar cookbooks. Butternut squash puree mixed in with the mac and cheese, for example.
Remember that it often takes a child about 8-10 tries with a new food to develop a liking. Also textures are sometimes tough for kids so try as many ways as possible to give them the same food. Soups, tacos, and a dip on the side are all ways to get kids to eat veggies in different forms. A lot of kids like a "salad bar" set up so they can take a little of everything - make a game of it.
And decorate with food - make a smily face on a piece of toast or on a small tortilla, for example. Red pepper slice for the smile, carrot "coins" for eyes, cauliflower floret for the nose, broccoli florets for the earrings, shredded lettuce or raw spinach for the hair, and so on.
I put everything in pancakes - you'd be astounded!
Try not to give a child a separate meal from what you're eating. Yeah, right - I know, easier said than done.