The leading cause of dehydration in pediatric patients is vomiting and diarrhea. These conditions result in a significant loss of fluids and electrolytes from the body, which can rapidly lead to dehydration, especially in children due to their smaller body fluid reserves.

Inadequate fluid intake can contribute to dehydration, but it is usually secondary to losses caused by gastrointestinal symptoms. Excessive sweating and diabetes insipidus are less common causes in the pediatric population.

It is crucial to recognize that children are more vulnerable to dehydration due to their higher metabolic rate and proportionally larger extracellular fluid volume. Prompt identification and management of vomiting and diarrhea are essential in preventing severe dehydration and its complications.

Reference: Pediatrics, 10th Edition, Volume 2, Chapter 25 - Fluid and Electrolyte Disorders, Page 432