L.F.
My daughter used to be the exact same way - only she was 3 instead of four and now she is 5 and still has issues with eating to the amount of my liking.
she is already small framed, long and lanky and in the bottom if her weight chart but top of her height chart....
So if you didnt know better you would almost think she was malnurished....
however, after trying not to force feed her and worrying about her losing weight - her dr suggested eating at the table and getting into a routine. Allowing her to help make dinner (mixing meatloaf, stirring the salad, picking hte veegie and so forth) - If she still didnt eat - dont give into the fits anf demands of junk foods... leave stuff on a plate that wont spoil - and give the nutrition drinks like pedia-sure... so that if the child doesnt eat - they still get the nutrients they need... but only at one meal - and juice or regular mimlk at the other meals.
Savannah out grew it for a while and now that she has started kindergarten and has only 30 minutes to eat - she is back to almost nothing - so I pack a bunch of snack foods she likes in her lunch box, like salads oranges and berries and nuts.... I dont force the meats on her - but on occassion she will ask for her fried chicken or something
Good luck and dont worry too much about it - as long as they are drinking good - even when they appear to not be eating - they will be fine and outgrow it - at least for a while.
Savannah kinds floats back and forth with her eating habit...