How well I identify with this request! My own son, now 7, is still among the world's pickiest eaters! Thank goodness he has expanded his menu choices a bit since he was your son's age, and will now eat a few fruits and vegetables. He still refuses meat except for a small bit of chicken now and then. Trying to draw his appetite away from the carbs to which he is naturally attracted has been a difficult process. It takes a long time to make a little progress, and in our family, time is always in short supply!
Here are a couple of things we have tried over the years. As a result of these food games, he will now happily eat broccoli (only raw, never steamed, and it must be untouched by any cheese or dip!) and cantaloupe -- two foods that most young picky eaters tend to avoid. He learned to eat bananas with these food games, and many of the other limited food items he now enjoys were first tried in this manner. Maybe you will have a little success, too.
A warning: These techniques require allowing the child to play with his food, so if that bugs you, these techniques will not work for you! My very good friend could not stand to see anyone play with food, and she was appalled by what we did at our table. But then she was never desperate; her kids ate brussel sprouts, beets and spinach from the time they were old enough to sit at the table. :) Personally, I never thought a messy and creative table was half as bad as a poopy diaper, and I saw plenty of those.
THE FARMER GAME: My son really liked to drive little cars and tractors around so I let him bring them to the table for the farmer game. We put vegetables out in the "fields" and I let him drive the (washed) tractor around for the farmer to harvest the peas and corn and carrots and other vegetables and deliver them to his plate. He never did eat the peas, but the other vegetables did get tried. He liked the broccoli best, because he liked to chop down the trees, eat all the leaves off first, and then tackle the trunk. He still laughs about eating "little trees." You may be washing mashed potatoes out of the back of little tractors for a couple of years, but if it's worth to you to get your son to try new foods, go for it!
FOOD FACES: This one is a tried-and-true food game. Set out a variety of foods and use them to create funny faces -- then try to eat the parts of the face. If your son is like most little boys, he'll giggle and be entranced by the notion of eating hair and eyes and ears, etc. The first few times you do this, make sure to use something sweet and tempting to your son as part of the face. Switch out the food items every time you do this so that he will be exposed to many different food items. Eventually, when you serve your son carrots, you will be able to refer to them as "noses" and when you serve him bean sprouts, you will be able to call it "hair." He will laugh and laugh when you say, "Are you going to eat hair or ears for dinner tonight?" If you slice bananas in small circles one time and use them for eyes, and leave them in long lengths the next time to become a mouth, you can eventually get to the point where you hold up bananas in the grocery store and ask your son, "Hmmmm. Eyeballs or lips?" He'll giggle along with you at the joke.
Eventually, when you are packing his lunch for school, you can ask questions like, "Would you like me to send noses or ears into school with your eyeballs today?"
Use a sugar cookie or a pancake for your first face to whet his interest and attract his sweet tooth, but don't keep using sugar cookies and pancakes or you will defeat the whole purpose! As soon as you find some other face part that he likes, move on and substitue pita circles or rice cakes to build the faces. Tell your son your goal is to create 100 different faces using 100 different food items --and when you reach your goal, you'll go see a movie or take a trip to the toy store.
Here are some food face ideas:
Funny Hair:
Bean Sprouts
Pasta died with food coloring
Broccoli or cauliflower flowerets
Baby spinach leaves
Eyes:
Chocolate Covered Raisins centered on circle-shaped banana slices. (Make the eyes "cry" with drops of honey. Most young kids love to do this!) You can also draw on eyebrows or eyelashes with chocolate syrup. But again, it's good to start with the sweet stuff and quickly move on to try to create eyebrows out of vegetables...
Cucumbers
Round scoops of cantaloupe or honeydew melon
Grapes
Mouths:
Cantaloupe slices
Banana lengths
Cherry Tomato halves
Red bell pepper strips
Noses:
Carrots
Canned pear (Shaped a lot like a nose, actually -- and since these are sweet, this a good one to start with)
I don't mean to sound disgusting, but little boys in particular are fascinated by gross humor, and this really peaks at ages 6 to 8. Many of them love to play around with Food Faces by adding raisins to the noses to become (you guessed it!) "boogers" or adding a little "nose hair" by sprinkling shredded cheese pieces on a sliced pear. Then it's fun to eat the gross face created. Shredded cheese is always good for becoming "whiskers" on funny faces.
Good luck to you in your quest to expand your son's menu choices. Remember, here in the trenches of mommyhood it takes a cast iron stomach, steely resolve, creativity and a bit of time to accomplish a goal-- and it sometimes helps to know there are many other moms in the trenches with you!