*This post is not meant to be judgemental in any way.......raising kids is the toughest job out there, bar none! This is just the way I was raised because we didn't have much and you were thankful anything was even on your plate.
I am all for exposing your kids at an early age to a variety of foods. I have 3 children (14,12,8) and although they LOVE mac and cheese (and my son loves chicken nuggets) they are some of the best eaters out there. At home, they simply don't have too much choice. I try to feed them healthy things but I am also trying to please them. We sit down as a family to eat most nights for dinner together. My standard line, said in a calm voice, if they complain about what they are eating is, "if it were monkey brains I was feeding you, I would understand. This is good food and mommy only makes one dinner. You can eat it or go to bed, it is your choice. " Now, I have 3 kids that eat better than their Daddy.

(Ignore all this advice if you have medical issues,etc. I don't have that so I can get away with it)
BUT, that is all done AT HOME. At a restaurant, on vacation, with everyone tired and hungry, and tired and hungry people all around you is NOT the place to push things. If my child insists on a certain thing that I KNOW the restaurant has available, why wouldn't I want to give them that? They are on vacation also. I certainly get what I want!
Most of the time when we are on vacation, my kids order pretty well. But if on that day they want mac and cheese for the 2nd time in a row or chicken nuggets instead of cold chicken pieces (like some of the counter service), I say go for it!
And I would also say to the server if they "suggested" that my child try it first, "so, if my child doesn't want it, is the grilled cheese sandwich going to be out in 30 seconds so they get to eat with the rest of the family?