My son is a picky eater. He won't eat a hamburger/cheeseburger, he won't eat a taco, he won't eat spaghetti and meatballs, never near a crustible thing., doesn't even eat eggs. At home he eats what I make, but if I make spaghetti and meatballs,he will eat just the spaghetti, plain, no sauce. He does not like spaghetti sauce, he hates ketchup. He has tried all of these things, just doesn't like them. We don't eat fast food at home, he gets a cooked meal every night. He is just pickey. I will make him try new things, but if he doesn't like it, I can force him to eat it.
But I find that most sit downs in WDW will accomidate. Even if there is nothing on the menu he will eat, if I ask the server, I can get him something. I have not had a problem yet. He will eat chicken and rice, or turkey. He is a big fruit eater, loves tomates (weird since he won't eat ketchup or tomato sauce) and loves cucumbers. Even in the QS places, There seem to be enough options that I can get him something he will eat. He does like the chicken nuggets and the mac and cheese, but I won't let him eat that the entire vacation.
Than there is my daughter, who will pretty much eat anything and everything. She is not picky at all. Sometimes flavors that are a bit more grown up- and she loves it. Here are two kids, brought up in the same household, that have two extreme eating habits. Sometimes its not the parents fault. kids will be kids.
On a side note, I do think having a big kids menu would be great.