 By the time a child is thirsty, he or she is already dehydrated. Some of the symptoms of dehydration are a dizzy or lightheaded feeling, decreased urine, or urine that is dark yellow instead of clear or light yellow. If a child is dehydrated, place them in a cool area and give them cool, but not icy, water or sports beverage. For Here's to Health, I'm Dr. T. Glenn Pate.