C.,
As far as I have been educated it is important that a baby over 6 months of age eats the baby cereal (rice, oatmeal, barley or mixed) because they have depleted their iron stores by that point and need the extra iron. The portion size is on the box but I believe by age six months it is either 4 tablespoons or 1/4 cup. Other than the breastmilk/formula and cereal the rest of the food is just for learning what the baby likes/dislikes. My son just turned one and he went through stages where he either loved or refused just about everything...cereal, veggies and meat. He has always loved fruit though. Have you tried giving fruit?
Be assured though that under 12 months the most important nutrition for the baby is the breastmilk. As long as he eats enough of that, he should be a healthy and happy little boy! =)