Dehydration is a loss of body fluids, which are made up of water and salts.
When sick children vomit or have diarrhea, they can lose large amounts of water from their bodies and can become dehydrated very quickly. Healthy children can spit up, vomit, or have a loose stool once in a while without being in danger of dehydrating. Dehydration can be very dangerous, especially for babies and toddlers. Children can even die if they are not treated. Diarrhea is a very common problem in childhood.