What Causes Aversion To Food In A Child?

Hi, My granddaughter is 2 yrs + 9 more old. She is a very happy, extremely smart little girl. The problem is that she never wants to eat very much and she only weighs 26 lb. She turns her nose up at mostly everything that is offered, but won t refuse sweets. My son and daughter in ,awhile have very healthy meals and not very munch junk food at all. She sleeps about 1p hr a night and takes a good nap, like 2 hr each day. She is all potty trained. My concern is that she does not take in very much food at a time and for a whole day does not eat like 3 full meals. Just worried that there may be something wrong...