Yikes, already! My son is like that but he didn't start until he was a little older. Or pediatricians usually suggested not to push him (to not cause anxiety about food) and to keep putting lots of variety in front of him. Unfortunately, that has not been helpful and he is still as picky as can be. He just snacks.
But, I have noticed when he has growth spurts he is more inclined to try something new. So we kind of really work with him then and then back off when he's not so hungry. He is 9 so it's not working quickly at all. I'd love to hear more advice on this as well.