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. Two or three 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. This is discussed in my diarrhea blog, but a couple quick notes here. Definitely avoid fatty and sugary food and drink as these will make the diarrhea worse. A short break (2-3 days) from milk may be worth a try, especially if the diarrhea is prolonged (e.g. 1 week or longer). Yogurt, however, tends to be well tolerated. If you are breastfeeding, definitely continue! The breast milk is beneficial. The BRAT diet (bananas, rice, applesauce, and toast) is a time-honored but often misunderstood diet. I find that parents sometimes think they should give this diet alone, but that should not be the case. While it is helpful for bulking loose stools, it is not particularly nutritious and if given alone for days can cause malnutrition. Give it in conjunction with fruits, vegetables, whole grains, and lean meats.
Milestones Pediatric & Adolescent Care 