A nurse is assisting with the admission of a 2-year-old toddler who has acute gastroenteritis. Which of the following actions should the nurse take first?

A. Determine if the toddler is voiding: Assessing urine output is crucial for determining the child’s hydration status. Voiding is an important indicator of kidney function and fluid balance. Ensuring the child is voiding can help determine the severity of dehydration and guide further interventions. B. Request evaluation of the toddler's serum electrolytes. Evaluating serum electrolytes is important for understanding the extent of dehydration and electrolyte imbalances. However, it is not the immediate first action and should follow the initial assessment of the child's hydration status. C. Initiate isotonic fluids with 20 mEq/L potassium chloride. Initiating fluid therapy is crucial but should only be done after assessing kidney function through urine output and evaluating the need for potassium supplementation to avoid complications like hyperkalaemia if the kidneys are not functioning properly. D. Collect a stool sample from the toddler. Collecting a stool sample is useful for diagnosing the cause of gastroenteritis, but it is not the immediate priority. The focus should first be on assessing hydration status and initiating appropriate fluid therapy.