Poor Appetite
It is quite normal for a child to have a decreased appetite when ill. If you think about it, most of us adults do not have a normal appetite when ill. People can survive a few weeks without food, so 2 or 3 days with a poor appetite poses no grave danger. 2 or 3 days without fluids, on the other hand, can be deadly, especially if there are fluid losses from fever, vomiting, diarrhea, or excessive urination (in a diabetic or child with sickle cell disease).
Everybody, adult or child, has fluctuations in weight from day to day. We look at a child's growth curve over an extended period of time to gauge how well he/she is growing. If we charted weight daily we would all go crazy with worry (just think how your own scale plays mind games with you)! A child who lost a pound during an illness will make up for it later, rest assured, unless there is a more chronic problem going on.
Don't force your child to eat, but calmly offer anything healthy he/she might nibble on. Resist the urge to offer cookies and M&Ms "just to get her to eat something", you will pay for that later. If everything is refused, don't panic. Try again later.
Of special note is the child with vomiting and/or diarrhea. Certain foods, such as dairy products, may actually make it worse, although this is still debated. A short break (2-3 days) from dairy may be worth a try, especially if the diarrhea is prolonged (e.g. 1 week or longer). One exception to this is the breastfed baby; continue breastfeeding, the breast milk is beneficial.The BRAT (bananas, rice, applesauce, and toast) is a time-honored and also debated diarrhea diet. It may also be worth a try, but do not use it for more than a few days as some nutritional deficiencies may result.