Is there an actual fear of trying something new?

My stepson is 10. He refuses to try new things and when he is "made to" he works himself up to the point where even if he does like he..he won't....he makes faces, gags, cries, and puts on a big show. This is almost always true when it comes to fruit and veggies and even things fruit flavored! Like strawberry wafers or strawberry ice cream. I am concerned with his health, like his vitamin and mineral intake! He won't take a multivitamin either! He only eats junk food, chocolate pancakes, chocolate poptarts, hot cocoa, sweet tea etc...at dinner, he'll eat the meat and pasta or potato side but not rice. I don't know what to do, my husband allows this and if I try to get him to try a carrot or corn niblet, I get undermined. I don't know what to do...a lot of my problem with his eating habits besides his health is that my 2 sons are required to eat what is in front of them and if it's new, they have the 3 bite rule...Any suggestions??