Some fruit and particularly some vegetables just don't taste good to children.  As they get older some of these fruits and vegetables actually start to taste good to them.  I know this because my son had to have a "no thank-you" helping (one small taste) of everything that was served.  He has told me often how glad he is that we did the "no thank-you" helpings because a lot of the foods he didn't like early on, he now really likes.  For years when he was a child, he would only eat the vegetable corn.  Now he has a wide variety that he enjoys.  Same with fruit.  I think the key is to not force children to eat things that just don't taste good to them.  The "no thank-you" helping is very, very small and pretty painless so the child doesn't feel the need to rebel against it.