C.-
I have two pretty close together so I know mealtimes can be stressful. Here are some things we do, I'm not sure if they will work for you, but who knows right?
1) we do smoothies but add ground flax and wheat germ. We use whole milk yogurt in them also to up the caloric and fat intake (fat is important at this age for brain development) .
2) We give lots of choices. It is kind of a pain, but eventually she picks something.
3) Foods we have had luck with... sliced or cubed avocado, beans (black, pinto, kidney), apple slices with almond butter, we add a granola to her yogurt, and also add flax seed and wheat germ to her yogurt. Other off the beaten path foods that worked were extra firm tofu cut in cubes( plain or sometimes with a little soy sauce), avocado rolls, edemame, sweet potato fries.
4) We do meals in Stages- I don't wait for the whole meal to be done. I also try to put the food she is least likely to eat on her plate first (meats for us). Also we don't abide by breakfast foods for breakfast or dinner for dinner... eggs or yogurt is a popular dinner with us and she has had a burrito or tacos for breakfast many times!
5) whenever it is safe we let her help. Sometime we just give her a bowl and some of the ingredients to play with while I cook.
I hope any of these help a little. Also remember to look at the eating on a whole. Some days are good and some days aren't, but over all they will get the food that they need if you provide it to them :)
Good luck and email me with any questions you might have.