Another big concern for parents is diarrhea. Defining exactly what constitutes diarrhea is tricky; it's probably best to think of it as a bowel movement that's significantly more frequent and watery than usual.
Diarrhea in babies is usually caused by a virus. One type, rotavirus, is responsible for most cases of diarrhea in kids. Rotavirus usually shows up during the winter in kids between 6 and 24 months. Once rotavirus takes hold, the only thing you can do is make sure baby stays hydrated. Your pediatrician would need to perform a test on baby's stool in order to make a definite diagnosis.
If your baby has diarrhea that just won't go away for more than two to three weeks and she lacks fever or cold symptoms, she could have a milk allergy. In addition to watery stools, allergic babies may be colicky, suffer from cramping when they have bowel movements, have small amounts of blood and mucus in their stool, and develop a rash. Most allergic babies get better once put on a hypoallergenic formula such as Nutramigen or Alimentum.