Ok I wrote a hub on this one so maybe check that out. Don't add sugar and crap to it thats just dumb. What kind of vegetables are you using? Are they fresh or frozen? How do you cook them? Do you steam or boil them?
I found with all seven of my kids that if you steam fresh vegetables they are more likely to eat them (four out of seven were troublesome at the dinner table.)
If youaren't winning there try cooking things like spaghetti bolognese, lasagne, quiches and stir fries. With those just dice the vegetables up into very small pieces and cook away. If none of that works then, I would say you have a behavioural issue (by that I mean they just don't want to and would rather argue with you about it) Take a look at my hub https://hubpages.com/family/help-my-child-wont-eat
That might give you some good ideas
Dont give up and good luck