i have 21 month old twins, my son is 21 pounds and 31 inches, the pediatrician said he is underweight, he and his sister were born at 33 weeks, he has virtually stopped eating, we have tried pediasure, etc and he is still barely eating, he does eat yogurt, i am worried, i am trying to cook new things and its not working, he will chew it an spit it out, i spend an hour or so at each meal trying to get him to eat something, he twin is 32 inches and 22.5 pounds, but much more solid, my son has gained nothing since feb, what can i do