What is the differential diagnosis in the below case study?

Jimmy is a 3-year-old “picky” eater

according to his mother. He refuses to eat anything but waffles for breakfast and macaroni and cheese or chicken nuggets for lunch and dinner. He will eat apples and bananas but refuses all vegetables except corn. After a normal physical examination, you obtained blood testing that revealed the hemoglobin is 11.4 mg/dl and his hematocrit is 30% (both obtained by venipuncture). The CBC revealed microcytic hypochromic RBCs.