Dehydration is a condition that develops when bodily fluids are depleted because of vomiting, diarrhea, high fever or excessive sweating. Children, especially toddlers, are more susceptible to dehydration because their bodies weigh less and turn over water more quickly than adults do. In most cases, dehydration can be treated by offering your child fluids frequently when he is sick. When a child is very ill and cannot keep fluids down, hospitalization may be necessary so she can receive fluids intravenously. At it's most severe, dehydration can be a life-threatening condition.