I'm not convinced that vitamins are the solution to picky eating behavior! As my grandmother once said, "they haven't figured out all the nutrients in food yet". This still holds true. Two year olds are busy exploring the world and perhaps don't need as much food as you might think. You really need to look at food intak over the course of a week, not a day to get the big picture on your child's food.
I would take a big look at juice intake and toddler cookies and cracker intake. These are empty calories that can add up to no appetite at meal time. They are also foods that can be "damp forming" according to Chinese medicine. One of the best books I've got in my collection on this topic is "Keeping kids Healthy with Chinese Medicine" by Bob Flaws.
It will change the way you look at food. When I took a one year course in Chinese Herbal Medicine many years back, I thought I would be learning about herbs. Instead I learned about the properties of FOOD that go way beyond carbs, protein, fat, calories and vitamins.
This simple book by Flaws can really have a positive impact on your child's food and health for the next decade. Check it out!
I also have a downloadable e book on my website about Picky Eaters. Hopefully you won't need it! Don't worry about the vitamins, just keep your eye on the big picture, FOOD and all the nutrients will take care of themselves! We have no real research that shows weather these vitamins actually do anything. Most are synthetic petroleum derivatives.
Trust mother nature instead, she's been around a lot longer!
Good Luck!