Elijah never used to be a picky eater. He would eat pretty much anything put in front of him. Now he's deciding that he's not interested in a lot of his meal options any more. Even if we think we have him figured out, he'll suddenly go off something he used to love. Beans are the latest thing on the refusal list. Mashed cheesy potato is just about the only guaranteed meal to be downed without a whinge.
Apparently Daddy used to eat mashed potato and not much else as a child. Perhaps this is another case of "like father, like son".