The regulation of fluids and electrolytes plays an important role in the care of neonates and children due to their distinct physiology. Newborns, especially those born prematurely, have a higher proportion of body water relative to their weight, and their immature kidneys limit their ability to adjust to fluid or electrolyte fluctuations effectively. Additionally, they are more prone to fluid losses through the skin and lungs, particularly in the early days of life. Children remain susceptible to fluid and electrolyte imbalances during illness, fever, gastrointestinal disturbances, or after surgery. Fluid therapy in children requires an understanding of age-specific needs, daily maintenance requirements, and the replacement of ongoing losses. Knowledge of the distribution of body fluids and the functions of essential electrolytes like sodium, potassium, and chloride is essential for maintaining stable internal conditions necessary for organ function and growth.