Dear D.,
Don't worry so much. I know, I kknow, THEY always talk about a well balanced diet and making sure blah blah blah. Bear with me, I'm telling you that you are probably doing a great job and its ok to let it go. The fact of the matter is, until we train it otherwise, the body knows what it needs. I never forced food on my little one and she even went through a period where I'd offer her anything other than carrots and she'd refuse. The important thing is simply to offer it. Her carrot craze lasted a week or so and then she was on to the next thing. (That was at about 8 months).
I actually teach nutrition to teens and we make it far more complicated as adults than it needs to be. Think of it this way, there are a number of color categories in the food we eat, Red, purple/blue, orange/ yellow, white/brown, green that is dark, and green that is light, Most of us eat way too much white (potatoes, corn actually counts as white, rice, bread, etc.) If by the end of the week you have had each of the colors twice and then your snacks and such are usually fruits or veggies you are doing REALLY WELL.
Back to your little one, He is still nursing too right? Or at least on a balanced formula? That means right now he is learning to eat for the purpose of learning to eat and supplementing the nutrition you give him. Offer him fruits and veggies. If he only takes the veggies, be glad he is accepting those and know he is getting what he needs.
I also suggest First Meals by Anabel Karmel. Each chapter is a particular age range, (so it will grow with you) she has suggestions about what to think about for nutrition for each age group, and does a great job with offering up recipies that are delectable to the kids and have a mixture of fruits, veggies, grains and colors all in one meal in a way that is fun or appropriate for the age group at hand. PLUS she identifies which meals (especially as they get older) are good for things like, freezing ahead, taking on a picnic, etc. and the recipes usually take 20 minutes or less to make.
My two year old loves fruits and veggies but definitely prefers the fruits. I offer her what I can and by the end of the week if I go over what she has eaten, its usually fairly balanced in terms of being a varied and colorful diet. She recently went through a period where all she wanted for three days were pears (in addition to pancakes with yogurt in the morning - I use yogurt instead of syrup unless I put fresh fruit like berries or peaches on top). Now, she wants strawberries, or oranges, tomorrow it will be green beans. Her body is telling her what she needs and she is listening because I'm not forcing anything on her and this has always been the case. She is healthy, active and happy. Just teach your son to listen to his body (of course this means avoiding sugary foods for as long as possible so they don't get addicted to the sugar), and when she asks for something sugary - like a cookie -I offer something more healthy first - she usually takes it without any argument at all and is completely satisfied.
Just keep up the good work and let your son tell you what he needs by choosing (to the extent he can) what he eats. He won't starve and he is choosing pretty healthy foods anyway if its the veggies he likes. Veggies are some of the most healthy, nourishing, well-packaged foods we eat!
Let me know how it goes!
R.