My son just turned 8..........we have this problem even though he doesn't have ADHD or anything! He's just AFRAID to try new foods! Poor guy. He ate great as a baby, but not after 3yrs old.
I just try to be creative with the few foods he'll eat, and come up with "enticing names" to help him try things. He likes peanut butter, so when it's on toast we call it "Peanut butter Pizza Toast" because he wishes he liked pizza :O) LOL! Whatever, at least he eats it.
I also make milkshakes out of pediasure and ensure (whatever is on sale). It rests my mind that he's getting more nutrition.
My older son (now 13) was a picky eater until about 9, and now he eats almost anything, and not afraid to try new foods. I pray that this will be my younger son, too.
I hope this rests your mind little knowing that there are other kids out here not eating well, yet still doing OK nutritionally.
Just try to go with it for now..........
~N. :O)