S.M.
Kid's tastes change so much as the grow. My son is the same age as yours and won't eat a veggie to save his life, but can eat an 8 oz steak quicker than my hubby or I. Don't worry about the vitamins, as long as your son is getting a good variety of food in his diet he will be fine. Keep offering them though, he might decide to like them as quickly as he decided to not like them. Try Pediasure if you are worried he isn't getting his vitamins or Carnation instant breakfast. They are great since they have al the vitamins they need and it is only once a day. And they have different flavors. My nephew has been drinking those right before bed for 5 years now.