My house, my food. Outside of my house, up to them.
With that said, the boys aren't vegetarians, but they eat a wide range of vegetarian foods. They also know that want they get, is what they get. We have "restaurant" nights, where we will cook anything they choose, but usually we just go to a restaurant for that
I don't believe in short-order cooking for kids. Sure, a treat of that once and a while is fine, but when it's my turn to cook, I cook a meal for all of us. you don't like it, you don't eat it. But you don't get anything else.
The rules change a bit when they are old enough to make their own food. At that point, if we were all vegetarians and one stayed a meat-eater and wanted space in the fridge, I would obviously allow that. Same with the reverse (if we are all meat-eaters and 1 is a vegetarian, would make a space for them).
Now, when they are at school..........if they end up eating all gummy bears and pork chops at every lunch, that's their choice. At home, it's another matter.