The same vitamins and minerals can be found in a mix of fruits, fruit juice, and cereals. In fact, in the United States, even the popular highly sugared breakfast cereals are fortified with vitamins and minerals to help them sell. While we're on the subject of vitamins and minerals, these are ingredients that are needed in small amounts. You don't need to eat ton's of food to get your recommended daily allowance of vitamins. And most parents give their children a vitamin supplement as additional nutrition insurance.
Many children prefer vegetables raw, which is the way they have the most nutrient value.
If you provide a diet of nutritious foods, even if your child doesn't eat a lot or eat them all, he should be adequately nourished. The worst mistake you could make is to offer your child treats instead of food out of fear that your child will starve if he doesn't eat. Once you give a child with a small appetite junk food in place of meals, since his appetite is small, he will just continue to refuse food until he gets the treats he wants. That may provide calories, but it isn't nutritious. Even overweight kids can be malnourished if they live on junk.