Fever in children is defined as a rectal temperature ≥38.0°C (100.4°F); in neonates <28 days, any temperature ≥38.0°C is a medical emergency requiring full sepsis workup. Dehydration occurs when total body fluid losses exceed intake, and children are disproportionately vulnerable due to their higher body surface area–to–volume ratio, immature renal concentrating ability, and greater insensible losses. Missed dehydration progresses from mild (3–5% body weight loss) to severe hypovolemic shock within hours, particularly in infants. Top 3 nursing priorities: 1. Accurate dehydration severity assessment (fontanelle, mucous membranes, capillary refill, urine output, skin turgor) 2. Temperature management and source identification — never give ASA to a child (Reye syndrome risk) 3. Oral or IV fluid resuscitation titrated to clinical response, not just temperature alone Classic NCLEX trap: Assuming a febrile toddler who is playful and interactive is not seriously ill. Infants <3 months with any fever ≥38.0°C require immediate escalation regardless of appearance — a well-looking febrile neonate still needs blood cultures, LP, and empiric antibiotics. On the exam, writers often pair stable-sounding options with unstable data—notice the mismatch before you commit.