W.C.
There are three things you can't make a child do, eat, sleep, or pee and poop on schedule. (sigh) My son was a picky eater. He only ate white foods from the time he was introduced to solids--only whites. And the way I introduced new foods was to feed them to him morning, noon and night for a week--but they had to be white.
Finally when he was big enough to eat real adult food I put the food on the table, he could choose what he wanted and if he didn't like it so be it, and he went hungry until the next meal. And he was a tall good sized boy. I did this even when he was a teenager. He knew the rule and never complained about it.
Now as an adult he is 6'2" and nice looking.
I firmly believe that as long as the child is moving, active, learning, and happy he or she is probably getting enough food.