I am not necessarily advocating this, but when I was younger, you got what you were given. And if you didn't like it, you went hungry (or learned to swap with someone else). We were allowed one vegetable, one fruit and one other type of food we absolutely wouldn't eat, and we had to lump whatever else there was. I was allowed to not eat cauliflower and fish, but I had to have at least a little of everything else if they were put on my plate (i liked all fruit).

Like i say, it might not have been the best tactic, but in the long run, you need to think about how to tackle extreme fussy eating, because the longer you go along with it, the less likely they are to grow out of it and adopt a more varied diet.

Hope you get something sorted in the short term though.