My 6 year old son is a picky eater. He had some other health problems that lead to that (he is now and has been fine since he was 2), but he Dietician from Children's kind of giggled at my list of foods he would eat and told me "well, what we have NOW is picky eaters syndrome". That was when he was 2-3 years old, and I have just accepted it. I take him to the grocery store with me (morning time was best he wasn't as cranky). I ask him if he would would eat this - or that. If he grabbed for something, I would buy it in hopes that he would eat it, and most of the time he would, and then lose interest. My son's Dietician/Nutritionist suggested a book called "How To Get Your Kid to Eat...But Not Too Much" by Ellyn Satter. She is a Dietician and this book addresses picky eaters and kids who eat too much.
Actually, Peanut Butter and Jelly Sandwiches is one if the best things for him, the Peanut Butter has protien. My pediatrician told me he had (the patient is now in college) who growing up, would only eat Corn Flakes, morning, noon, and night. He ate them with Milk, but his mom kept bringing him into the pediatricians office and wanted him evaluated at Children's Hospital (which he was and they told her nothing was wrong with him, etc. just let him eat Corn Flakes). The family all got really sick from a flu virus, and the only kid that didn't get sick from the family was the one who ate Corn Flakes. True Story.
Foods that have worked for us: Stoneyfield Farms Yogurts in a tube (they are like Go-Gurts only they are organic and better for your little one, my son used to eat these 3-4 times a day)
Grapes, Macaroni and Cheese (Swanson frozen individual ones that are a perfect serving, and none goes to waste, and, it tastes better than the instant, boxed stuff). Honey Nut Cheerios (plain is too plain)
My son is now 6, and since he was 4 we have tried to reason with him in making him try something new, we told him that every night. He is given what we are eating, and then I'll make him Mac & Cheese if he refuses or gags on what we are eating. He now love Chicken Drum Sticks and Broccoli -cooked with cheese on it (he loves broccoli who knew) He is the only child in the produce section who begs for broccoli, I get it for him of course. He also likes pizza, fries and chicken nuggets. When he was 2-3 he would beg for fries from McDonalds-if he was having a "non-eating" day where he litteraly wasn't eating much, I would cave and get him fries from McDonalds, but that was only once a week, maybe once every 2 weeks, it wasn't a daily thing.
Good Luck-hang in there! It will get better-I promise. It's mostly trial and error with picky eaters.
37 year old SAHM of 2 boys ages 12 & 6. Have been married for 17 years.